Should you take a COVID-19 antibody test? Currently, no. Wait a second! Won’t the test tell me whether I’ve been exposed to the coronavirus? Possibly…..or possibly not. Only three tests have been approved by the FDA and the accuracy of these tests remain a mystery. As we’ll explain below, there is only one circumstance in which you should take an COVID-19 antibody test. And in no circumstance should you pay for taking such a test.
Not only are these antibody tests not-ready-for-prime-time, but in some circumstances they could be dangerously inaccurate — leading people to believe they are, or are not, susceptible to COVID-19 infection. Perhaps the question that any consumer should ask before coughing up money for an antibody test is: Am I willing to risk the life of a loved one by taking a test that might only be accurate 20% of the time , as the city of Laredo, Texas recently discovered?
What Is A COVID-19 Antibody Test?
Here’s what it most certainly isn’t – it won’t tell you whether you have a COVID-19 infection. Instead, it is a serologic (blood) test that will tell you whether you have the IgM and IgG antibodies in your blood stream. Serologic antibody tests can only confirm suspected cases after the fact, not necessarily if you have an active case. These tests are useful because as many as 25% of the public with a COVID-19 infection may be unwittingly spreading the virus because they have mild or no symptoms. They may also be useful to scientists and politicians who are making important decisions about reducing commerce restrictions.
Makers of these antibody tests are selling them to businesses and doctors. The New York Times reports that thousands of Americans have already taken them, costing a patient roughly $60 to $115. The majority of the tests currently on the market are manufactured in China.
What’s Wrong with the Current Antibody tests?
No one knows the accuracy of the current tests! Why take a test when there’s an unknowable likelihood that the results will be wrong? Although commercial manufacturers claim their tests have high sensitivity and specificity, they haven’t published their data yet. And because most all of the tests have been rushed into the marketplace, people who use them are more guinea pigs than they are patients. So, to answer the question of why you’d pay someone to give you a test that is probably wrong? You wouldn’t.
Worse yet, most people with COVID-19 don’t start producing antibodies in the blood until at least 11 to 12 days after symptom onset. So if you think you’ve recently had the disease, it is likely that a serology test result would be inaccurate.
Most of the test results will be unreliable largely because so few people currently have been exposed to the disease. Social distancing measures have not only “flattened the curve” but they’ve largely shielded the majority of people from coronavirus exposure. While that is a desireable outcome, it royally screws up antibody testing. Say you are running a test that gives five falsely positive results in a group of 100 people. That’s a 95% reliability factor which sounds promising. But consider the fact that if only 5% of those 100 people were actually infected with the coronavirus, you will get only correct test results (true positives), along with the five false positive results. In this very likely scenario, the antibody test will be wrong half of the time!
And even if tests are reliable, they can’t indicate whether someone is immune to reinfection. This is but one of the many reasons why the World Health Organization currently warns against taking a COVID-19 antibody test. The agency warned on April 17th that: “there’s no evidence serological [antibody] tests can show whether a person has immunity or is no longer at risk of becoming reinfected.
As of early May, the Federal Drug Administration has finally begun releasing results of its own tests on some of the antibody tests. The results of their analysis can be found here — and they suggest that not all tests are accurate. The first COVID-19 serology test granted an Emergency Use Authorization by the FDA—Cellex’s lateral flow rapid test, using drops of blood and a test strip similar to a pregnancy test—showed a combined sensitivity of 93.8% and a specificity of 96.0% when searching for two different antibodies linked to the coronavirus. According to Fierce Biotech, at 5% prevalence, that equates to a positive predictive value of 55.2%. At 10% prevalence, that estimate of performance increases to 72.3%, while at 2.5%, it drops to 37.6%. Again, it appears that the test results depend heavily on prevalence. In the U.S., we simply don’t know the prevalence numbers at the moment because of our testing deficiencies.
Other products use different testing technologies and examine larger blood samples—such as the high-throughput ELISA tests developed by Abbott, Roche and other companies. Roche’s recently authorized Elecsys test showed 100% sensitivity and 99.8% specificity across multiple antibody types, with a positive predictive value of 96.5% and a negative predictive value of 100% at 5% prevalence. Similarly, Abbott’s Architect test for IgG antibodies showed a sensitivity of 100%, specificity of 99.6%, and positive and negative predictive values of 92.9% and 100%, respectively. If you are considering using any of these 12 FDA-authorized tests, you should check the FDA website here.
So, Who Should Take a COVID-19 Antibody Test?
If you are a health care professional or an emergency first responder and you are offered to be part of a scientific study of an antibody test, it may be worth your time to do so. Also staffers at nursing homes may want to avail themselves of a test study. But you shouldn’t have to pay a dime for participating in such studies.
Ultimately, government officials and health systems need accurate infection counts to understand COVID-19’s spread, conduct contact tracing, craft public health recommendations, and prepare for health care surges. When the dust has settled, epidemiologists will use widespread testing data to more accurately estimate just how many people who contracted the virus became seriously ill or died. At that point, we may be able to restore commerce and open up our locked-down communities. However, that will likely be months, if not a year away.
Currently, the National Institutes of Health–funded antibody survey is enrolling 10 000 volunteers from around the country and, according to news reports, nationally representative, CDC-funded serosurveys are slated to begin later this year. Researchers in Germany and Italy are reportedly conducting large-scale antibody testing, with Germany planning to issue “immunity certificates” to transition its citizens out of lockdown. Public Health England, which provides evidence-based support to the National Health Service, recently discussed plans for nationwide antibody screening that would begin once a rapid, at-home finger-prick test under consideration was assessed for accuracy. Sadly, the White House hasn’t announced similar plans, instead deferring to individual states to conduct testing.
Ultimately, a positive antibody test could be a sort of “get-out-of-isolation” card. But we are no where close to that. As Michael T. Osterholm, an infectious disease expert at the University of Minnesota. noted in a recent New York Times article: “We’re not even in the second inning of a nine-inning game at this point.”