Autorefractors: Can They Really “See” Clearly Themselves?

Autorefractors were designed based on Caucasian eyes, and this bias is factored into the measurements.

by Brian Zhou

“Open your eyes.”

Growing up in a small Midwestern town, I have heard many prejudiced phrases intentionally or unintentionally directed at me. However, I never expected to feel uncomfortable because of my race in the optometrist’s office.

Autorefractors are devices used to measure the refractive error of light passing through the eye when light passes through the eyeball and is reflected back to the instrument. This measurement is made to determine whether a person is near-sighted (myopic) or far-sighted (hyperopic).

An image is projected into the eye from the device, and the light passes through the cornea, pupil, and lens, and finally bounces off the retina and returns to a sensor in the autorefractor. The autorefractor then processes the reflected light beam, making a prescription for the eye from the distortions it picks up from the reflected light beam.

Originally developed by NASA to measure the vision of their pilots, autorefractors quickly became an alternative to traditional retinoscopy due to their accuracy. Due to their speed of diagnosis, ease of use, and repeatability, autorefractors became widely used.

In terms of usability, autorefractors are not suited for people with monolids. Being Asian, I have monolids with longer eyelashes. This makes it particularly difficult for the light rays to reach my eyes and then bounce back to the sensor for an accurate readout. Often, at the optometrist office, I have gotten so frustrated with myself that I tried to physically hold open each eye with my fingers. As a 7-year-old child, it was hard to keep still in the chair, push my forehead up to the bar as much as possible, and keep my eyes as wide as possible without blinking for each measurement.

For me, these measurements took up to 20 minutes to complete, and when I observed other patients from the waiting room go in and out of the room quickly with their prescriptions printed on the paper, I began to realize it was just me. I started to think that I had a problem with my eyes. Maybe they were abnormally small? It took me years to realize that monolids were natural, and honestly, the first time I even realized that other people had issues with autorefractors too was a college medical device design course, when I shared my experiences.

Autorefractors were designed based on Caucasian eyes, and this bias is factored into the measurements. Retinal vertex curvatures were shown to be different for Asians than Caucasians, which may be a reason why there is a higher prevalence of myopia in Asian countries compared to Western countries. Since the autorefractor test was designed for

Caucasian lenses, the refractive error it measures may not account for different eye shapes, which may explain errors in diagnosis.

Technicians have gotten frustrated with me because my eye shape was not cooperating with their machine, and they gave up and just used whatever result they could get. Experiences like these may contribute to a potentially high misdiagnosis rate of myopia in Asians. Ultimately, due to fundamental biases in its design, the autorefractor is not a good eye prescription test for many Asians. While genetics may also be a reason why Asians have higher rates of myopia, further research into autorefractors and how they measure the refractive error for different eyes is needed. We must question and wonder whether these machines can truly see through an unbiased lens.

More to Read:

1. Gurnani, B., & Kaur, K. (2022). Autorefractors. In StatPearls. StatPearls Publishing.

2. Kilfoil, D. (2015, October 6). What is an autorefractor? Coburn Technologies, Inc; Coburn Technologies.

3. Li, T., Zhou, X., Chen, X., Qi, H., & Gao, Q. (2019). Refractive Error in Chinese Preschool Children: The Shanghai Study. Eye & Contact Lens, 45(3), 182–187.

4. Padhy, D., Bharadwaj, S. R., Nayak, S., Rath, S., & Das, T. (2021). Does the Accuracy and Repeatability of Refractive Error Estimates Depend on the Measurement Principle of Autorefractors? Translational Vision Science & Technology, 10(1), 2.

5. Rong, S. S., Chen, L. J., & Pang, C. P. (2016). Myopia Genetics-The Asia-Pacific Perspective. Asia-Pacific Journal of Ophthalmology (Philadelphia, Pa.), 5(4), 236–244.

6. Szczotka-Flynn, L. B., & Efron, N. (2018). Aftercare. In Contact Lens Practice (pp.364–384.e2). Elsevier.

7. Verkicharla, P. K., Atchison, D. A., Suheimat, M., Schmid, K. L., Mathur, A., Mallen, E. A., Wei, X., & Brennan, N. A. (2014). Is Retinal Shape different in Asians and Caucasians? Estimation from Peripheral Refraction and Peripheral Eye Length Methods. Investigative Ophthalmology & Visual Science, 55(13), 3592–3592.

How We Got Here: The 2021-22 Supreme Court Hearings in Texas and Mississippi Abortion Cases

Before we begin posting about the science and technology aspects of abortion, we thought we would go over the recent history.

On Monday night, Politico published a leaked draft of the majority opinion in the Supreme Court calling to overturn Roe v. Wade.1 If the opinion becomes finalized this summer, it will end the forty-nine-year precedent of federal abortion protection and an individual’s right to choose.  Before we begin posting about the science and technology aspects of abortion, we thought we would go over the recent history.

The year 2021 saw a historic peak in legislation surrounding abortion in the United States, with 108 restrictions passed by the end of the year.2 One such restriction that raised concern was Texas Senate Bill 8 (SB8), brought to the Supreme Court on November 1 as United States v. Texas. The Supreme Court heard a second major lawsuit against Mississippi’s 15-week abortion ban on December 1, Dobbs v. Jackson, culminating in this latest draft opinion, the authenticity of which was confirmed by the Supreme Court on Tuesday.3 In light of both lawsuits, I will summarize the differences between the Texas and Mississippi cases and the implications the leaked, unfinalized opinion holds for Roe v. Wade.

First, it is important to understand some of the terminology commonly used in these cases. Abortion laws target different developmental milestones during the gestational period, as a major point of contention between pro-choice and anti-choice advocates is, “When does life begin?”

In general, fetal viability refers to the period between 22 and 24 weeks of pregnancy. This was determined as the point at which a fetus can survive outside of the womb, as approximately 50% of premature babies can live past this stage in development.4,5 This occurs during the second trimester and is used in twenty states as the point until which elective abortion is legal.6,7

Last September, Texas enacted a type of legislation termed a “heartbeat bill,” restricting abortion to the first six weeks of pregnancy since this is when a fetal heartbeat can first be detected. However, this developmental marker is debated within the scientific community.

In 2018, Mississippi introduced a bill banning abortion after the first trimester (15 weeks), claiming that dilation and evacuation, a surgical abortion procedure, is more dangerous than giving birth after this point.8 However, UCSF Health cites surgical abortion risks during the second trimester as having fewer and less serious risks than birth,9 and many studies have proven that legal abortion is safer than live birth.10–12 Furthermore, the Turnaway Study showed that individuals who sought abortions but were denied care were more likely to face physical, mental, and economic challenges in the future, with ramifications for all children in the family as well.12–14

So, What Is Texas Senate Bill 8 (SB8)?

What does the bill state?

The bill bans abortion after approximately six weeks and incentivizes civilians to sue anyone involved in providing or aiding an abortion after that period. Plaintiffs will receive at least $10,000, paid by the defendant, if successful in the lawsuit. While patients themselves cannot be sued, anyone who drove them to the hospital, funded, or performed the procedure falls under the law. Additionally, doctors who are sued must report the lawsuit(s) when reapplying for their medical licenses.15

How does this contribute to other restrictions in Texas?

Even before SB8, Texas already had many other abortion restrictions. The addition of Senate Bill 8 will increase driving distances to access abortion clinics fourteen-fold, as calculated by the Guttmacher Institute.16 Additionally, Texas is one of thirteen states that have passed “trigger bans,” which will automatically go into effect banning all, or almost all, abortion if Roe v. Wade is overturned.17,18

What did the Supreme Court decide?

On December 10, the Supreme Court released their 8-1 decision, allowing the Center for Reproductive Rights, a pro-choice organization, to continue their case against SB8 in the lower courts. As the Supreme Court did not move to block the bill itself, it will remain in effect unless overturned by the U.S. District Court.19  In the wake of this decision, many other states, including Oklahoma, Arizona, and South Dakota, began to produce copycat bills of SB8, seeking to limit abortion access to six weeks of pregnancy or less in anticipation of Roe v. Wade being overturned this summer.

How Does this Relate to Mississippi’s House Bill 1510 (Gestational Age Act)?

Although many abortion restrictions have been said to contradict Roe v. Wade, the Gestational Age Act poses the biggest threat to overturning the 1973 landmark case. When the state petitioned to have Dobbs v. Jackson heard by the Supreme Court, they emphasized that the case was only about the legality of the 15-week ban, but during the hearing on December 1, the state centered their argument on the need to overturn Roe v. Wade. Chief Justice Roberts termed this tactic “bait and switch.”20

If the outcome of Dobbs v. Jackson is to overturn Roe v. Wade, Texas, Mississippi, and many other states will move to completely ban, or to severely limit, abortion services. Oklahoma, for example, has passed SB612, which criminalizes abortion as a felony except when the pregnant individual’s life is in jeopardy; the bill is set to go into effect on August 26.21 Not only will the removal of Roe v. Wade inhibit bodily autonomy, but it will likely have a disproportionate impact on those who do not have the financial resources to travel out of state. 

While those who seek abortion represent a range of reproductive ages, classes, races, gender identities, and family dynamics, most are living in poverty, in their twenties, and already have at least one child.22,23 Clearly, increasing abortion restrictions would make it more difficult, if not impossible, to get care for those already burdened by social determinants like inconsistent access to transportation, lack of childcare services, and inability to take time off work and lose pay.

Furthermore, the comparative risk of live childbirth is more severe in Black individuals, who have up to a 450% higher risk of death than white individuals.24–27 This will cause devastating consequences if states enact stricter abortion limitations or bans, forcing higher numbers of unwanted pregnancies to be carried to term despite the enormous risk of death in doing so.

The apparent end of Roe v. Wade is quickly approaching, and it is a catastrophic loss for reproductive rights in this country. However, with midterm elections occurring this year, it reemphasizes now, more than ever, why every vote matters, especially to support pro-choice candidates at the local, state, and congressional levels. Furthermore, Abortion Finder, Planned Parenthood, and other pro-choice organizations are continuing their fight to support individuals looking to end their pregnancies,28–30 and the National Network of Abortion Funds is managing donations that will support travel and associated expenses for those who must go out of state to seek care.31 Large businesses must also consider including abortion aid in employee benefits, as Yelp, Citigroup, Match Group, and others have done.32


1.        Supreme Court has voted to overturn abortion rights, draft opinion shows – POLITICO.

2.        State Policy Trends 2021: The Worst Year for Abortion Rights in Almost Half a Century | Guttmacher Institute.

3.        Supreme Court Live Updates: Roe v. Wade Draft Decision Leaked – The New York Times.

4.        When Is It Safe to Deliver Your Baby? | University of Utah Health.

5.        Periviable Birth | ACOG.

6.        States with Gestational Limits for Abortion | KFF.,%22sort%22:%22asc%22%7D.

7.        State Bans on Abortion Throughout Pregnancy | Guttmacher Institute.

8.        Bill Text: MS HB1510 | 2018 | Regular Session | Enrolled | LegiScan.

9.        Surgical Abortion (Second Trimester) | Conditions & Treatments | UCSF Health.

10.      Raymond, E. G. & Grimes, D. A. The comparative safety of legal induced abortion and childbirth in the united states. Obstetrics and Gynecology 119, 215–219 (2012).

11.      Darney, B. G. et al. Quality of care and abortion: beyond safety. BMJ Sexual & Reproductive Health 44, 159–160 (2018).

12.      Gerdts, C., Dobkin, L., Foster, D. G. & Schwarz, E. B. Side Effects, Physical Health Consequences, and Mortality Associated with Abortion and Birth after an Unwanted Pregnancy. Women’s Health Issues 26, 55–59 (2016).

13.      The Turnaway Study | ANSIRH.

14.      The Harms of Denying a Woman a Wanted Abortion Findings from the Turnaway Study.

15.      Bill Text: TX SB8 | 2021-2022 | 87th Legislature | Enrolled | LegiScan.

16.      Impact of Texas’ Abortion Ban: A 14-Fold Increase in Driving Distance to Get an Abortion | Guttmacher Institute.

17.      Texas abortion access on the line as Supreme Court reconsiders Roe v. Wade | The Texas Tribune.

18.      Abortion Policy in the Absence of Roe | Guttmacher Institute.

19.      Supreme Court of the United States. Whole Woman’s Health Et Al. v. Jackson, Judge, District Court of Texas, 114th District, Et Al. (2021).

20.      What Happened at the Supreme Court Arguments Over the Mississippi Abortion Law – The New York Times.

21.      Oklahoma Lawmakers Approve Near-Total Ban on Abortion – The New York Times.

22.      Demographics | Guttmacher Institute.

23.      Induced Abortion in the United States | Guttmacher Institute.

24.      Texas’s New Abortion Law Will Harm People of Color, Further Entrench Racist Policies | Commonwealth Fund.

25.      Racial and Ethnic Disparities Continue in Pregnancy-Related Deaths | CDC Online Newsroom | CDC.

26.      Black Women Over Three Times More Likely to Die in Pregnancy, Postpartum Than White Women, New Research Finds | PRB.

27.      Hoyert, D. L. Maternal Mortality Rates in the United States, 2019. (2019) doi:10.15620/cdc:103855.

28.      I need an abortion.

29.      Where Can I Get an Abortion? | U.S. Abortion Clinic Locator.

30.      Planned Parenthood on Supreme Court Leak: Our Worst Fears Confirmed, Supreme Court Appears Poised to Overturn Roe .

31.      Home – National Network of Abortion Funds.

32.      Yelp joins growing list of companies offering workers help with abortion care – CNN.

My “Reverse Graduation” Speech

I had a chance to welcome the class of 2025 this week. The ceremony took place in the large and well ventilated arena with thousands of masked and vaccinated students looking on. A bit scary, but a milestone to be sure. Everyone had to have a negative PCR test to enter. They put me on the agenda right behind the student speaker who is a speech and debate champion….not nerve wracking at all! Anyways, here is what I said (slightly edited):

Wow, class of 2025! You made it! Some say showing up is half the battle. But this year, showing up is a complete, hard-fought victory. You’ve done a lot to get here, and we have been working hard to make sure that the university is the best and safest place for you to be right now. I’m going to tell you a little of the story about how people across this great university, some of them with us here today, came together to make welcoming you and your families possible.

But first let’s talk a bit about how stunning it is to be here all together in this place after the last 18 months. This is certainly an intense way to get back into speaking in front of students! The last time I gave a speech like this was at my 8th grade graduation in 1986. Our class of about 50 graduated that year and went on to enter a regional high school class of almost 1000. 35 years later, I have no idea what I said, and the notes are lost to history, but I remember being terrified.

There could have been a nugget or two of advice from a 13-year-old me that might have been helpful to you today – but not likely much. You have already lived a life that I could hardly have imagined in 1986. You have endured a pandemic, the sometimes-explosive reexamination of racism in this country, the pressures of climate change and more. Coming of age in this time and place has challenged your mental and physical health, strained your finances, and for many of you has meant the loss of family and friends.

I must tell you, while this has been a tiring two years, we know you enter college hopeful and full of high expectations for yourselves and for this place. We aim to meet those high expectations and make your time here rewarding and life changing.

The town I grew up in was about ten times smaller than the population of this university! I am sure that this is true for many of you as well. We all come to this place from other places, and we bring our memories, traditions, and hopes with us. You have moved from something smaller to something bigger, with more opportunities that you can imagine. Those opportunities are accessible online to be sure, but many of the serendipitous meetings and experiences that will change your life can only happen in person. When I was a freshman at Northwestern University, I was planning on being a journalism major. I had been the editor of my high school newspaper. I had not taken any science AP courses, since my high school counselor didn’t think that would be useful for someone who wanted to be a writer. But during freshman orientation week, I had some time to kill, and I was wandering around campus. I bumped into a tour at the engineering school and followed along. I found myself in a small dark room watching a scientist use a scanning electron microscope. After that tour I changed my mind about my major and re-registered for engineering classes. What was she looking at? What minute wonder of the universe caused me to change the direction of my entire life? She was watching cement dry. Hardly Earth shattering! But it was cool, and it was small, and it was beautiful to me. I wanted whatever my job was to involve studying the world at that size scale. A serendipitous meeting. A life changing moment. It could only have happened in person.

Those moments await you around every turn. The expansive and collaborative nature of this place is what makes it great. In my 18 years here I have run a research laboratory that has been home to students from engineering, the college of arts and sciences, the school of public health, and the school of medicine. In my lab, we work to bring new technologies for miniaturized medical diagnostics to underserved or unserved populations. My involvement in this work is how I came to be the Scientific Director of the Clinical Testing Laboratory.

Soon after we went remote, it became clear to many of us that with the available knowledge at the time that the university would not be able to open safely in fall 2020 without routine molecular testing for COVID-19.

In April 2020, the university president sent me an email.

Dear Cathie,

I hope you are safe and well. I suspect, like me you are about to go crazy staying at home. [Note this was only 5 weeks into lockdown!]

…I am very interested in pulling together the resources to do high throughput testing for COVID via PCR.  We don’t have a great deal of time to have this up and running by mid-August.  The project needs organization and leadership. Are you interested in being involved?

Please let me know…

I responded immediately in the affirmative. After all, my entire professional life had been focused on diagnostic testing. My lab works on making these tests small and accessible to communities without highly instrumented laboratories. Although I had spent my entire career up to April 2020 trying to make things that do not require sophisticated laboratory equipment, it was immediately clear that to keep the university open, such laboratory equipment would be required.

For the first couple of weeks, our team was small. Members of my laboratory were quickly joined by colleagues in Electrical and Computer Engineering. Our expertise in molecular testing combined with theirs in programming liquid handling robotics set the foundation of the team.

The earliest work, during a time when the dangers of contracting COVID-19 were still largely unknown, was done by graduate students, post docs, and a couple of newly minted grads. Together we built a plan, tracked down costs, interviewed suppliers and gathered information from teams that were starting similar projects at other colleges and universities around the country.

Once the president gave us the go ahead to proceed, our team grew to include lawyers from the general counsel’s office to help us navigate the regulatory landscape. Soon after that we needed the procurement group to help us secure the necessary equipment and supplies in a very uncertain marketplace with rapidly changing supply chains. Next, we had to leverage the facilities and building management apparatus of the university to set up places to collect up to 6500 swabs a day. As we worked, people on other teams reinforced student and employee health services, upgraded ventilation systems, redesigned move-in procedures, made and posted thousands of new signs, communicated our plans to the community, worked with the city and state departments of public health, and built new IT systems to make all of it work together.

It wasn’t a perfect roll out, but it was very very good. This project was the most challenging and, in my opinion, the most successful and rewarding project of my career.

Twelve weeks later, In July 2020, we delivered our first test results to students on the medical campus. By the end of August, we were routinely testing everyone on campus at least once a week.

By now you have all interfaced with the system that was put into place over those 12 weeks. I took my 14-year-old daughter with me when I dropped off my last test, and when we walked out she said, “That was it? They just scanned the tube?” I was a bit disappointed. Didn’t she want to know about those days last July when we frantically were calling the graphic designer at the company supplying the tubes because they did, in fact, not just scan? About any of the other road blocks and challenges that were coming at us like a firehose those first few months? Of course not.

All of the difficulties and minutiae that we dealt with, and the team continues to deal with, were invisible from the vantage point of the end user. As any good engineer or designer knows, the end user just needs the system to work. It needs to work so you can go to class, play sports, put on dance recitals, attend studio classes, or work on problem sets late into the night knowing that you are doing these things in the safest possible environment.

Nearly every time we needed to add people to the project with a particular skillset, we had those people already here, and they were eager and ready to serve. I encourage you to look closely as you spend time here at all the things that just work. The chairs set up in this room, the sound system amplifying my voice, the entire schedule of today’s events were all planned weeks and even months in advance. We have been waiting to welcome you and eager for you to contribute to this place in your own unique way.

These four years will pass by quickly, but they will be some of the most influential years of your life. The only certainty is that you will change. Many of you will change your major, like I did! Some of you will change it more than once! Some of you will change your pronouns. You will meet lifelong friends. Some of you will meet life partners. You are entering into an exciting new world of ideas.

I have certainly changed during my 18 years here. When I first arrived here I used walk by students during move in and see parents hugging their children goodbye. I saw all these new beginnings –  these launches of young people into a new phase of life. Now that I am a parent, as my girls approach college age themselves, it’s harder for me to watch families say goodbye. In fact, it now brings tears to my eyes. Interacting with the world in this way allows us all to appreciate our shared humanity. I’m sure we all appreciate being together again now more than ever.

The class of 2025 is remarkable already. As you enter this next phase of your life and education, I wish you the very best. Welcome. We are so very glad that you are here.

From the Dalkon Shield to Britney’s IUD

The answer is that the reproductive health of people who can get pregnant is simply not a high enough priority in our society. We settle for good enough when we could have great. 

Last week Britney Spears described how under her conservatorship, she was required to be fitted with an intrauterine device and is prohibited from removing it without her father’s permission or the permission of the court. Presumably the goal was to stop Ms. Spears from becoming pregnant with additional children without the express authorization of her custodian. 

Britney Spears from her Instagram Page.

There are many discussions to have about Ms. Spears’ rights, disability rights, and forced reproductive control. The topic is an intersectional minefield. An amazing discussion with a journalist who is an expert in the field and who has a disability was broadcast on What Next this week. My own thoughts on the subject would require me to use profanity on a blog that I know is read by my program manager at the NIH, and when I resort to profanity, that usually means I am out of comfortable intellectual waters. What I can discuss with a fair amount of authority is the IUD itself, its history in modern times, and how it has succeeded and failed as a medical device for people who want to avoid pregnancy. 

If you are my age (49) or older, you first learned about the IUD from horror stories told about the Dalkon Shield. The Dalkon Shield was an IUD invented in the early 1970’s by a gynecologist. Hugh J. Davis, was known as an intellectually arrogant person who didnt take criticism well.  So, it wasn’t a very inclusive design team – just one man. He later recruited Irwin Lerner, an electrical engineer, to help him finalize and market the device.  The device was rushed to market with insufficient clinical data, and the inventors published their pre-market data without acknowledging their financial interests in the device. They sold the device design to the A.H. Robins company, and Davis continued to act as a consultant and proponent of the device for many years. 

At the time, the birth control was popular, but the high levels of hormones in those pills were concerning to many.  The side effects of the pill were and still are troublesome and sometimes very serious. In the 1970’s, the available pills nearly 100 times more progestin and 3 to five times as much estrogen as what typical combination pills contain today.  Second, and probably more important, is the fact that the A.H. Robbins company did something new that we now take for granted: they marketed the ever loving heck out of that device. 

Dalkon Shield Marketing Material

Before 1976, you could invent and patent a new medical device that was meant to be inserted inside a uterus and worn for years at a time with absolutely no federal oversight. As a result, there were no regulations that limited or specified the set of materials to be used to construct the device. So, when the company decided to use a new material for the string, they were able to make that change without consulting any oversight body or performing additional testing to make sure that it was safe. 

It turns out that the filament they used for the string was made up of several smaller filaments, like a cable consisting of several smaller wires wrapped together. The little spaces in between the multi-filament string were small enough to give bacteria from the vagina a pathway into the uterus. These bacteria caused infections in people wearing the device that were later recognized as pelvic inflammatory disease. All told, the Dalkon Shield resulted in the injury of hundreds of thousands of women and the documented deaths of at least 18. 

The Dalkon Shield disaster is why medical devices are now regulated by the FDA, due to a federal law passed in 1976. Prior to 1976, only drugs were regulated. 

As a result of the Dalkon Shield injuries, deaths, and related lawsuits and finally recall, IUDs fell out of fashion in the US. Even though many other non-Dalkon devices existed, the market for IUDs was non-existent. The FDA approved the first new generation IUD in 1984, and that device was available in the US in 1988. Then several years passed before the current crop of modern IUDs began to come on the market from 2001-2016. These are considered Class III medical devices and require pre-market approval before they can be sold in the US. 

If a device failure occurs, doctors and patients are encouraged to report the failure to the FDA. Only distributors and manufacturers are required to report. The FDA compiles a database of these failures and though the reporting system is largely voluntary, the FDA does investigate to see if they are part of a pattern. Even the devices containing copper are considered to contain a drug, so must undergo stricter regulations required of drug/device combination products. Most agree that this has led to a very safe but short list of new generation IUDs available in the US. The downside of this enhanced regulation is that many devices approved in other countries that may be more appropriate for some people are not available here. The cost of obtaining FDA approval is too high to make selling in the US market attractive to foreign manufacturers. 

The stain of the Dalkon Shield has faded a bit. Younger people are more likely to seek and IUD as a long-term reversible form of birth control.  However, the legacy of birth control designed, developed, and marketed by people who cannot become pregnant is still a part of medical care today.  All the highly effective birth control methods have undesirable side effects. (Well, maybe not vasectomies, but that requires a monogamous relationship with someone with a good amount of self-knowledge and foresight for maximum efficacy – a rare situation). 

Everyone else must figure out what side effects and inconveniences we are willing to deal with to manage when we do and do not want to bear children, if at all. Why is the situation so dire? Why do we take the pill and risk life threatening blood clots at rates that are higher than those that temporarily stopped the use of some vaccines during a global pandemic? The answer is that the reproductive health of people who can get pregnant is simply not a high enough priority in our society. We settle for good enough when we could have great. 

One way to make better contraceptive choices a priority is to have people who can become pregnant directly involved with the design and development of contraceptive devices. Involved from the earliest stages. We need the viewpoints of these people as patients and as clinicians, designers, and engineers.  And we all need to think just a little more about each other’s healthcare. 

Simply, when the people who are the main users of a technology are not consulted in the design phase of that technology, the results for the end users are subpar and sometimes outright harmful. 

Diverse teams can save lives.   

As for Ms. Spears, it seems clear that her autonomy has been robbed without due process. Since you cannot remove an IUD on your own, she is effectively at the mercy of the state with respect to her ability to bear more children. Medical science may have given her a safer device than was available in the 70’s, but disability law has kept her rights in the 1920’s.

You are going to stick *what* up my nose? [Update with TikTok links!]

These are not your grandmother’s nasal swabs.

To continue our recent discussions on disease testing, today we’re talking about swabbing and swabs. 

Perhaps you’ve been lucky enough to experience a swab test firsthand. As testing becomes more widespread, we are all likely to have a nasopharyngeal swab taken for a  COVID-19 test. When I was a child, maybe around seven, I remember going to the doctor’s office to be tested for influenza, another virus that replicates in the nasopharynx. When the nurse first pulled the slim, wire swab out of the packaging, I thought no way. No way that daunting, 5-cm long wire will fit up my nose. Sadly, I was mistaken. I won’t lie – it wasn’t the most pleasant experience. The tickling sensation lingered in my throat long after the swab had been removed. I still felt it even after my results had come back – negative, luckily for me. Just a common cold! 

This kind of swab is referred to as a nasopharyngeal swab, which I learned many years later. Nasopharyngeal swabs are used to collect samples from the back wall of the nasopharynx (hence the name), which is where the nasal passages meet the throat. Other common swab tests include nasal swabs and oropharyngeal (throat) swabs.

Nasal swabbing vs. nasopharyngeal swabbing from link.

Swabs are made out of a number of different materials. Since the nasopharynx is much farther back in the nasal passage, the swab needed to get there must be longer and somewhat bendable. The swabs used for sampling the nostrils and throat are generally stiffer and shaped like long Q-tips. The materials that comprise the tips of these swabs are different, too. If you are trying to get material out of the oral or nasal cavities for testing, you need a surface at the tip that is good at grabbing that material. It is also important to be able to wash the material off and into the testing solution when needed. Thus, regular cotton is often not suitable. 

In terms of COVID-19 testing, the swabs you’re most likely to encounter are nasopharyngeal and nasal swabs. Nasal swabs are less invasive. The swab only needs to be inserted 1 cm into the nostril and rubbed along the septum for a few seconds. Nasopharyngeal swabs, on the other hand, require a longer swab, which is inserted about 4-6 cm back into the nostrils (about half-way between the entrance to the nares and the base of the ear). The swab is then rotated inside the nasal passages and left in place for a few seconds to absorb the sample. 

Check out Dr. Klapperich demonstrating anterior nares swabbing (AN) here and here on TikTok!

Swabs made to sample the nasopharynx usually have a tip made of plastic foam, or another material with lots of surface area. These are called “flocked” swabs. Only a few factories in the world make these swabs, which is why you regularly hear about swab shortages for testing. Sadly, using a version of a regular Q-tip would not be a suitable replacement. There are a number of innovative groups around the world looking for ways around this shortage. Some of them include 3D printing swabs made from medical grade plastics. All swabs that are used to apply topical medications or collect fluid samples are considered Class I medical devices by the FDA

In studies comparing the sensitivity of nasal vs nasopharyngeal swabs for influenza, nasopharyngeal swabs were found to be slightly more sensitive (94% vs. 89% sensitivity). This means that for the flu, a nasal swab sample will lead to a false-negative test result more often than a nasopharyngeal swab. But despite their inferior sensitivity, nasal swabs are simpler and useful for “self-swabbing”- taking your own sample to send or have delivered to a testing facility. According to the most recent update to the CDC’s COVID-19 specimen collection guidelines, nasal swabs taken by a healthcare worker or via self-swabbing are acceptable if taking a nasopharyngeal swab is not possible. But these guidelines are sure to change as more information comes out about how swab type affects false-negative rates for COVID-19. Early indications are that nostril swabs are not as good as nasopharyngeal swabs for this new virus. 

The Racialized History of the Spirometer

A spirometer is a medical device often used to assess respiratory function and diagnose respiratory diseases, including asthma, chronic obstructive pulmonary disease, and asbestosis.1 To use the device, you inhale and exhale as deeply as possible into a breathing tube attached to the spirometer itself, which measures your forced vital capacity (the maximum amount of air you can breathe in) and forced expiratory volume (how much you can breathe out in 1 second).1 

Figure 1: This shows the basic set-up of a modern spirometer test. The patient wears a nose clip and breathes into a mouthpiece, and a monitor displays a graph of their inhaled and exhaled volume. (Source Wikipedia)

For each patient who is tested using a spirometer, the operator must enter information about the patient, including their age, sex, height, and race.2 Unbeknownst to many operators, selecting a patient’s race enables a “race correction” setting programmed directly into the spirometer software – typically a 10-15% lower baseline lung capacity for patients identified as Black, and 4-6% lower for patients identified as Asian.3 Despite conflicting studies contesting the validity of using racial correction factors,4 it continues to be taught in modern science. This idea that non-whites have intrinsically lower lung capacity began as a justification for slavery, and the ramifications of this notion have continued to manifest in modern-day medical devices. 

In Thomas Jefferson’s “Notes on the State of Virginia,” the former president and slaveholder described deficiencies in “the pulmonary apparatus” of Black slaves.5 Plantation physician Samuel Cartwright further elaborated on Jefferson’s sentiments with his own spirometer studies, reporting a 20% “deficiency in the negro” in regards to lung capacity.6 Cartwright promoted slavery on the grounds that forced labor was necessary for Black people’s health due to their innately lower lung capacity. He stated that “it is the red vital blood sent to the brain that liberates their mind when under the white man’s control.” 6

After the Civil War, Benjamin Apthorp Gould further expanded on Cartwright’s work by comparing the lung capacity of Black and White soldiers. Although Gould did not account for height, age, or the living conditions of recently emancipated slaves, Gould’s conclusions mirrored those who came before him: “full blacks” had lower lung capacity than “whites.” 2,5,7 Gould’s study is still cited in scientific articles today.2

Over the course of the 20th century, researchers continued to fuel the idea of innate racial differences in lung function, repeatedly failing to account for the influence of socioeconomic conditions. In a review of articles published between 1922-2008 comparing lung function between races, 94% of articles did not examine race in the context of socioeconomic status.8 Although it is often ignored in research articles, lower lung capacity has been associated with poverty in past studies, as well as other social determinants including environmental toxin exposure and healthcare inaccessibility.2,5 

In 1984, J.E. Myers published an article that questioned the body of data supporting innate racial differences in lung function. Myers conducted his own spirometer studies of Black workers in South Africa, and his calculations showed that the published South African standards considerably underestimated the lung volume of Black people.4 Myers also challenged the assumptions made in previous studies, pointing out that they neglected to account for socioeconomic factors including environmental pollutants, housing quality and nutrition quality.4 

Several years after Myers’ article, in 1999, asbestos manufacturer Owens Corning used the argument that Black people have an intrinsically lower lung capacity to evade lawsuits from Black workers with lung damage. The company tried to argue that Black workers should be held to a different standard when assessing asbestos-induced lung damage because Black people consistently score lower on pulmonary function tests.9 The motion was overruled, but the case highlighted how historic assumptions on race have infiltrated modern lung research. As in the case of Owens Corning, modified lung function standards based on race have the potential to reduce diagnosis rates for respiratory illnesses and lung damage. 

Current spirometers implement “race correction” automatically, defining race as a purely genetic difference, rather than exploring the environmental and socioeconomic factors that have been shown to influence lung function. Lundy Brahn, a Brown University professor of Africana studies and medical science, addresses these issues in her article “Race, ethnicity and lung function: A brief history,” where she provides insights on how to address lung function research in the future. 

“Research and clinical practice needs to devote more careful attention to the social nature of racial and ethnic categories and draw on more complex explanatory frameworks that incorporate disproportionate exposures to toxic environments, differential access to high-quality care and the daily insults of racism in every sphere of life that manifest biologically.” 2 

– Lundy Braun, PhD


1Spirometry: Mayo Clinic,is%20helping%20you%20breathe%20better.

2Race, ethnicity and lung function: A brief history, by Lundy Brahn

3 Breathing race into the machine: The surprising career of the spirometer from plantation to genetics, by Lundy Braun

4Different ethnic standards for lung functions, or one standard for all?, by J.E. Myers

5Science reflects history as society influences science: brief history of “race,” “race correction,” and the spirometer, by Heidi L. Lujan and Stephen E. DiCarlo

6 The Science and Politics of Racial Research, by William H. Tucker

7Investigations in the Military and Anthropological Statistics of American Soldiers, by Benjamin Apthorp Gould

8Defining race/ethnicity and explaining difference in research studies on lung function, by Lundy Braun

9Racial basis for asbestos lawsuits?; Owens Corning seeks more stringent standards for blacks, by Erin Texeira

Are pulse ox devices racist?

Black communities are already faced with substandard healthcare, so when a medical device that monitors vital signs, such as the pulse ox, is developed without Black and dark-skinned people in mind, it is much more than just a design flaw.

In our last blog post, we went into detail about pulse oximeters and their mechanism of action. As we touched on briefly, blood oxygen measurement varies greatly from person to person since it relies on light passing through tissue, which behaves differently depending on a number of biological factors. This seemingly objective method actually serves as an example of biomedical technology that fails to account for all of these factors.

We couldn’t find a single stock shot of a pulse oximeter being used on someone with dark skin at, we checked.

Low oxygen saturation levels, the type of sensor in the device, gender, and skin color have all been shown to cause errors in pulse oximetry, but the discrepancies relating to skin color may be the most glaring. Studies and extensive anecdotal evidence from clinicians have shown that any errors due to low oxygen saturation were more dramatically skewed in Black patients when compared to their white counterparts. More specifically, at oxygen saturation levels below 80%, pulse oximetry measurements are significantly overestimated in dark-skinned patients

At saturation levels below 80%, patients begin to experience oxygen deprivation to the point of organ failure (hypoxia). So, if a pulse ox reading is overestimated in a dark-skinned patient, a healthcare professional could easily miss the onset of hypoxia. This limitation of the technology is critical especially now, during the COVID-19 pandemic, which is killing Black people at a rate three times higher than that of any other racial group in America. Black communities are already faced with substandard healthcare, so when a medical device that monitors vital signs, such as the pulse ox, is developed without Black and dark-skinned people in mind, it is much more than just a design flaw. 

As engineers, we are taught that device design of any kind cannot be successful unless the product meets all necessary requirements. Just like designing a building requires every environmental condition to be taken into consideration, designing a medical device requires every kind of person to be taken into consideration.

Nevertheless, in the 1980s, when the pulse ox first underwent FDA screening, accuracy and calibration testing was conducted primarily on light-skinned people; this has not changed since then. Despite the major functional disparity, the FDA has yet to require further research and testing dedicated to developing a pulse ox that produces accurate measurements on darker skin.

To pulse ox, or not to pulse ox?

Another day, another COVID-19 discussion… 

With each passing week, we are learning more and more about how to deal with this pandemic, both individually and as a community. We are now well-versed with preventative measures like washing our hands frequently and wearing masks, but what happens if you actually start feeling sick? While the symptoms of this viral infection are varied, they usually include high body temperatures, dry cough, and shortness of breath. Most of us have a thermometer at home, with which we can easily diagnose abnormal temperatures. But, is that enough to detect the early stages of a COVID-19 infection? 

Pulse oximeters (pulse ox) are getting a lot of attention right now. If you have ever had surgery or if you have a respiratory condition like asthma, you likely know that a pulse oximeter is the little medical device that clips onto your finger and informs your doctor of your heart rate and how much oxygen is in your blood. Monitoring blood oxygen levels has been critical for COVID-19 patients because a drop in the amount of oxygen in your blood indicates the need for more aggressive interventions.  Since you can buy a pulse oximeter at the drugstore, many people are wondering if they need one at home. So why exactly do respiratory issues warrant the use of a pulse oximeter? 

When your lungs are functioning properly, around 95% – 98% of the blood in your arteries should be “oxygenated,” or carrying oxygen. Your blood carries oxygen with the help of hemoglobin, a protein that has the ability to bind to oxygen molecules. Hemoglobin is what  makes blood a great transporter of oxygen from your lungs to the other organs in your body. Without oxygen, your organs cannot function because they rely on a process called oxidative phosphorylation, which uses oxygen to produce the energy that drives all organ functions. When your lungs are compromised, like they are during a COVID-19 infection, they are unable to efficiently take oxygen in from the air and pass it into your bloodstream. As a result, your other organs don’t get enough of it to do their jobs. This condition is called hypoxia. 

The circulatory system. Red vessels are the ones that carry oxygenated blood.

Now, let’s get back to the pulse oximeters. A pulse oximeter measures the percentage of oxygen saturation in your blood by shining both a red light and an infrared light into the top of your finger. The bottom of the device has a sensor that detects the amount of light that passes all the way through your finger. You can visualize this mechanism by doing a quick little science experiment on yourself. Turn on your cell phone flashlight, put your finger on it, and see what happens. If red light shines through, your blood is probably not deprived of oxygen. Good for you! Oxygenated blood absorbs every wavelength of visible light except red, which is why the red light can go all the way through your finger. Deoxygenated blood, however, is really good at absorbing red light. Now, we can see how the pulse oximeter takes advantage of these properties of blood to give a measurement of oxygen levels. 

So, why is infrared light also necessary? Blood vessel width varies from person to person, making the volume of blood in the vessels vary as well. Only using red light would result in misleading oxygen levels because the readings would be affected by these varying blood volumes in different people. For that reason, infrared light is used alongside red light to normalize the measurement and adjust it to each user’s body. Infrared is not well-absorbed by either oxygenated or deoxygenated blood, so it is a good baseline comparison measurement. The pulse oximeter calculates the ratio of absorbed infrared light to absorbed red light to get the percentage of blood saturation. In oxygen-rich blood, the low level of infrared absorption divided by the similarly low level of red absorption results in a ratio close to 1, which is equivalent to a percentage close to 100%. As blood oxygen levels decrease, this ratio also decreases because the red light absorption (the denominator) increases while infrared absorption stays relatively constant. Readings below 92% indicate the beginning of a hypoxic state. 

How a pulse oximeter works.

The ability to detect hypoxia is what makes pulse oximeters critical for COVID-19 patients. Healthcare professionals who are currently treating these patients are finding that oxygen levels can drop well below 92% before patients have any trouble breathing. When a patient does finally go to the doctor complaining of shortness of breath, their infection and hypoxia may be very advanced. Often, symptoms like fever and fatigue can also mask early hypoxia symptoms. It is easy to get used to the mild shortness of breath or pass it off as fatigue while blood oxygen levels continue to drop. For these reasons, some doctors are suggesting that everyone should get a pulse oximeter to use at home so the onset of hypoxia can be caught early. 

A big disclaimer that many physicians are making however, is that pulse oximeters should be used at home along with thermometers and calls to your doctor. There are still many cases in which COVID patients do not present with any hypoxia, but have high fever and the telltale dry cough. So, blood oxygen level, while helpful, is not the only metric used in diagnosis.

So, should you buy a pulse oximeter? To put it plainly, it’s really up to you. If you are sick, you called the doctor, and they said you’re not sick enough to go to the hospital, it may be helpful to have one and monitor your own blood oxygen so you know if you ever do need to go in. You may want one in that situation just to keep your peace of mind. Even if you aren’t sick, and just want to be prepared, it definitely can’t hurt to get one. However, all the stories about hypoxia going unnoticed paint a scary picture. It’s important to remember that, if you can’t get your hands on a pulse oximeter right now since the demand is high, it’s not the end of the world. The vast majority of COVID patients are able to get diagnosed and get to the hospital in time if necessary just by calling a doctor. So, you really don’t need to buy that $200 pulse oximeter you found on Amazon. You can find them for about $30 at your pharmacy, but if they’re sold out, don’t panic! Just keep washing your hands, keep that 6-foot distance, and if you are sick, call your doctor. Here at the blog, however, we are device geeks – so any opportunity to have a new medical device around the house we’ll take! 

Can you really hack a ventilator?

“What did Elon Musk say this time?”: COVID-19 Edition

A few weeks ago, Elon Musk promised to purchase and send ventilators to hospitals experiencing equipment shortages. He faced backlash from the media after one of the hardest-hit hospitals in Queens, New York, tweeted a picture featuring one of the “ventilators” he sent – actually a BIPAP machine. Media outlets and Twitter users criticized him for sending these non-invasive devices rather than the life-support ventilators that hospitals desperately need. Was it a rookie mistake? Maybe. Let’s go over the differences among these medical devices that all interact with the respiratory system! 

You probably know someone who uses a CPAP (Continuous Positive Airway Pressure) or BIPAP (Bilevel Positive Airway Pressure) machine. Folks who have sleep apnea use them to sleep more safely and comfortably. When I was younger and would spend nights at my grandparents’ house, I was terrified of the CPAP mask that my grandfather wore at night, and the noises it made. Eventually, after scrutinizing the face mask and hose connected to the machine, I convinced myself that he looked like an elephant. I love elephants. CPAP machine fear: conquered.

CPAP Machine

BIPAP and CPAP machines are both non-invasive types of ventilators, not the type that are normally used in hospitals for patients that are oxygen-compromised. When we inhale, our diaphragms contract and flatten down towards our pelvis, allowing our lungs to expand and increase in volume. Throwing it back to high school physics – when the volume of a container increases, its pressure decreases. Air follows a gradient of high to low pressure, so when our lungs expand, the higher pressure air outside of our body rushes into our lungs. Ventilators generally help facilitate this process when patients need more oxygen in their systems, or their airways are compromised. CPAPs and BIPAPs deliver a constant stream of positive air pressure through the mouth and nose to keep airways open. Their main users, obstructive sleep apnea patients, need them to prevent the throat muscles from relaxing too much during sleep, so the airways can remain unobstructed. 

CPAPs can only be set to one level of pressure or slowly advance to a maximum pressure overnight, whereas BIPAP machines are a little fancier and customizable to provide support for users who need more oxygen saturation support, and higher air pressure. BIPAPs have two pressure settings – a higher one for inhaling, and a lower one for exhaling, because exhaling against a high, continuous pressure can be difficult and uncomfortable. 

Both of these assistive devices consist of a face mask covering the nose and mouth with a hose that attaches to the machine that performs all of the work. It is possible for patients with less acute cases of respiratory distress to use BIPAPs in hospitals, especially when ventilators are few and far between (more on why later), which is why Musk likely chose to send BIPAPs, rather than wait for more complex machines to be manufactured. However, CPAP and BIPAP machines can be dangerous for healthcare providers right now – leaky face masks can expose them to airborne virus particles, though it may be possible to mediate that risk by using some new innovations. 

Life-support ventilators are more invasive and complex. They have many moving parts, settings, and even customizable software, making them powerful enough to meet the demands of different conditions for patients with severely compromised lung function. Size and frequency of breaths can be monitored to manage a patient’s specific needs at all times. Slow, medium sized breaths are more beneficial for stabilizing respiratory distress than deep and slow, or rapid and shallow breaths. They also generate air pressures that are strong enough to hold open bronchioles, the small branched airways in your lungs, that can collapse under inflammation or fluid build-up – all complications of COVID-19. 

Patients who need ventilators are anesthetized while an endotracheal breathing tube is carefully inserted through the mouth and down the trachea (the windpipe), and a cuff is inflated around the breathing tube in the trachea to form a seal (like when you get your blood pressure taken). This is particularly important for COVID-19, as the cuff prevents virus particles from leaving the airway and exposing healthcare providers to the virus. Physicians must decide who gets a ventilator and who gets a CPAP or BIPAP based on the severity of a patients’ case. But, why do they even have to make that decision in the first place?


We are experiencing a global ventilator shortage due to a variety of factors, including significant disruption to global manufacturing supply chains (the resources and companies needed to manufacture products) as a result of the pandemic, and prior market demand. In 2019, before COVID-19, the entire world only needed 77,000 new ventilators a year. Now, manufacturers would need to increase their rate of production by 500-1000% percent in order to meet the demands of this public health crisis. Manufacturers have only been able to increase their production by about 30-50%. Life-support ventilators are incredibly complex and expensive machines; they require more than 700 parts that are often sourced from all over the world, and they cost about $50,000 each. Manufacturing plant size and supply chain disruptions prevent this process from accelerating to meet our needs. 

In order to combat the ventilator shortage, the FDA released new guidelines on March 22nd to allow hospitals to be more flexible with this life-saving equipment to meet the influx of cases of COVID-19 related respiratory distress. The guidelines allow small modifications in materials, software, or functionality to be made to pre-existing or newly manufactured ventilators without FDA approval. The guidelines also allow CPAP and BIPAP machines to be used for less-severe COVID-19 cases, with careful monitoring. The FDA specifies flexibility with materials for breathing tubes, which are now difficult to obtain, and ventilator motors, to increase the capability of less-powerful machines. 

Normally, these changes would need to pass through the FDA’s 510(k) pre-market approval for medical devices, a fast-tracked process that allows newly developed devices that are “substantially equivalent” to previously cleared devices to get approved quickly, without clinical trials. Now, manufacturers and hospitals have the flexibility to use modified devices without clearance for emergencies. The FDA emphasizes that the use of FDA-approved devices should be prioritized over the use of modified CPAP and BIPAP machines. In particular, they encourage the development of filters to protect healthcare providers from aerosolized virus particles when using CPAP and BIPAP machines for less severe cases, and new software to encourage remote monitoring of patients to prevent exposure. 

One example of this innovation is a group at UC Berkeley working to fit CPAP machines with endotracheal tubes and filters, eliminating the need for face masks and significantly reducing the risk of viral exposure. Ultimately, Elon Musk did the right thing here – he provided extra resources to hospitals in need. In fact, after the media backlash, Musk said that the hospitals confirmed that they had a critical need for BIPAP machines for less severe cases. Musk has also pledged to dedicate Tesla factories to manufacturing ventilators. Hopefully he and others can help refit BIPAP machines for safer use! 

Rendering of a sleep apnea device retrofitted to help COVID-19 patients. (Grace O’Connell image)

What we talk about when we talk about diagnostics.

After spending the last few weeks talking with students, journalists, neighbors and family members, I’ve decided that there might be some value in discussing some of the terminology that we use when talking about diagnostic testing.

Science communication and media relations folks always discourage “jargon” when describing scientific concepts to laypeople. However, technical terminology can be a key part of scientific discussions, especially when it’s important to be precise. Now, in the setting of a global pandemic, precision is particularly important, and I believe people can handle more complexity than the scientific community often gives them credit for. Increasing scientific literacy can empower people to better understand and digest current events. So, here are some of those definitions.

First off, is reagent. In general, a reagent is any substance that is a starting material for a chemical reaction. Do you remember finding the “limiting reagent” in high school chemistry class? That’s the chemical that runs out first; thus, limiting the amount of product that can be made by the reaction. Many outlets have reported that one of the reagents failed in the initial test that the CDC distributed for COVID-19. It is still unclear which reagent did not perform as expected, but the reagent was one of the parts of the test reaction that the CDC shipped out to labs around the country. This problem has now been fixed, and all of the CDC test components are working well. 

Negative and positive screening test cassette strips.

The next term is assay. Assay is just the word we use for “test.” Anytime you hear someone say they are running an assay or assaying for something, they are simply running a test. 

Controls and control material also come up often when discussing test design. Controls are needed to make sure that the test you are running is valid. Basically, controls are parallel experiments that you run alongside your testing to make sure that you didn’t make a mistake while running the test. We science folks are always skeptical and are always checking to make sure we didn’t make a mistake! A positive control, in the context of COVID-19 testing, is when we put some material in the reaction that we know will make the test come up positive. If that reaction does not come up positive, we know that we made a mistake someplace, or that some of our other reagents are not working properly. A negative control is when we set up a test that does not contain a sample or additional material, that we expect to come up negative. If a negative control comes up positive, then we know that we have some kind of contamination, or that something we did not expect is happening in our reaction. If this happens, we need to start over, and figure out what went wrong. In both cases, controls that do not work as expected render any test result invalid. These results are not reliable and should not be reported. 

Now, we need to cover sensitivity and specificity. These guys are a bit more complex. Sensitivity measures how little of the virus you can detect using a particular test in a particular sample. A super-sensitive test can detect very small amounts of the virus. Sensitivity goes hand in hand with the concept of a false negative. A test that is not sensitive enough might come out negative for someone who is infected with the virus, but does not have a viral load high enough to make the test read positive. It is also possible that a false negative can arise from a swab being taken improperly. 

Specificity is a measure of how well the test detects the COVID-19 virus, and not other things that might confuse the test. A very specific test is good at detecting COVID-19 and will not detect other closely related viruses. Specificity goes hand in hand with false positive rates. If a test is not very specific, it might show a positive result when someone is not infected with COVID-19, but with something else like a flu virus. 

Both false positives and false negatives make it difficult for healthcare providers to interpret test results in the context of care. Low rates of false positives and false negatives make a test more trustworthy. 

Now you know the basics of test design and metrics! We hope that this makes reading some of the science reporting a little more clear.