Updated May 21, 2020.
Media coverage about COVID-19 antibody tests continues to dominate the news as dozens of companies announce new solutions coming to market. Since the beginning of the pandemic, antibody tests have been touted as a way to identify people who are immune to COVID-19, and even as a way to reopen world economies by issuing digital “immunity passports” to people with detectable COVID-19 antibodies. However, a rising chorus of experts has cautioned against using antibody tests in this manner, citing limited scientific evidence linking antibody levels to COVID-19 immunity. We’re here to help you cut through all the noise and help you understand what antibody testing is, how it may be beneficial, and what its limitations are.
What are antibodies?
Antibodies, also known as immunoglobulins (abbreviated Ig), are infection-fighting proteins created by the immune system in response to the unique characteristics of the infectious agent. Over the course of an infection, the immune system produces different types of antibodies including IgM, which develops early in the immune response, and IgG, which develops later and can be a marker of immunity.
Because antibodies to a virus can only be produced if someone has been exposed to the virus (or to a vaccine, which doesn’t yet exist for COVID-19), the presence of antibodies to a virus is a good indicator that the person has been infected. IgM antibodies are produced by the body during an active infection, while IgG antibodies come later and typically signal the infection has passed. IgG antibodies may also indicate immunity, or resistance to reinfection with the same virus, as is the case for certain other viral diseases such as measles, hepatitis A and polio. We do not yet know what level of IgG antibodies are indicative of immunity to COVID-19, but research is underway and we expect to have an answer to this question in the future.
What is a COVID-19 antibody test?
A COVID-19 antibody test, also known as a serologic test, detects the presence of antibodies specific to the causative virus, SARS-CoV-2, in a blood specimen. The most accurate antibody tests involve a laboratory technique called ELISA (Enzyme-Linked ImmunoSorbent Assay), and require a vial of blood to be sent to a diagnostic lab with specialized equipment.
Alternatively, handheld “point-of-care” test kits need only a sample of blood from a pricked finger and can give results within minutes. There are over 100 versions of this kind of test being offered worldwide, and the accuracy of these kits is highly variable, leading the World Health Organization to recommend against using them except for research purposes until more information is available about their accuracy.
At One Medical, we’re working closely with our partners at laboratories like Labcorp, Quest and major academic health systems, as well as many manufacturers of point-of-care test kits, to identify the most reliable antibody tests we can offer to the greatest number of people.
How is antibody testing different from PCR tests?
The vast majority of tests conducted for COVID-19 to date in the U.S. have been PCR (polymerase chain reaction) tests. PCR tests detect the presence of genetic material from the SARS-CoV-2 virus itself, and therefore can reveal whether someone has been infected early in the course of the illness, sometimes days before they’ve produced any antibodies to the virus. PCR is reasonably sensitive for detecting an active or very recent COVID-19 infection, and it remains the standard tool for identifying and isolating people with COVID-19 before they spread it to others.
PCR cannot be used to reliably determine whether someone has had an infection in the past, because individuals who have completely recovered from COVID-19 often no longer have any virus in their bodies and will therefore have a negative PCR test result.
Most PCR tests for COVID-19 use specimens collected from the nasal passages or mouth.
What are the potential benefits of antibody testing?
Antibody testing can serve at least three important purposes. First, it can help identify people who are acutely infected with SARS-CoV-2, especially when paired with PCR testing. Antibody testing on its own is not accurate enough, since antibodies don’t develop until several days after an infection begins. But PCR testing isn’t perfect either, as it can miss up to 25% of acute infections. Combining antibody and PCR tests results may lead to improved sensitivity for detecting acute COVID-19 infection.
Second, antibody tests can help identify people who were previously infected with COVID-19 and have recovered. This is critically-important information for epidemiologists trying to understand how the virus spreads, how deadly the virus is, and how vulnerable a community might be to relaxation of social distancing rules.
Third, and most tantalizing, is the idea that antibody tests could confirm whether people are immune to COVID-19, either due to having recovered from the illness or due to vaccination (once a vaccine becomes available). Immune individuals would be able to interact with others without fear of spreading COVID-19 or becoming infected themselves, and would be able to serve essential roles in healthcare and in reopening the economy.
Most infectious disease experts think it’s likely that COVID-19 does induce some degree of immunity in those who recover from it, but this has yet to be proven. Whether immunity to COVID-19 might last a few weeks, a few years, or lifelong is also an open question.
What are the risks of antibody testing?
Like all diagnostic tests, COVID-19 antibody tests have important limitations, and using them indiscriminately can be risky. An isolated IgM antibody test might miss a case of infection, especially if the test is performed before any antibodies have formed. Such a “false negative” result might lead someone with an active infection to enter into a social setting or workplace and unknowingly spread the virus to others. The risk of a false negative result can be reduced by performing a PCR test at the same time as the antibody test, which is a combination we hope to offer at One Medical soon.
Conversely, an inaccurate IgG antibody test might mistakenly identify antibodies to a different coronavirus, such as one of the strains that causes the common cold, leading to “false-positive” results. Such results could cause susceptible people to believe they’re immune to COVID-19, and they might stop physical distancing measures and put themselves into risky situations where they could become infected. False positive antibody results could be a major problem with COVID-19 due to the fact that in most communities, only a small percentage of the population is believed to have been infected. The rarer the condition being tested, the higher the likelihood of false positive results.
Even extremely accurate antibody tests could still be dangerous, since we don’t yet know whether the presence of antibodies is indicative of true immunity. A person with a true positive antibody test result might conclude that they’re immune and stop physical distancing, only to discover that the antibodies weren’t actually protective and they’ve become infected again or infected others.
How will I know whether I'm immune to COVID-19
At this point, we lack any definite proof that immunity to COVID-19 is possible, though many scientific investigations are underway and we should have answers soon. Hopefully a simple antibody test will be able to identify people who are immune, but the test will need to be highly accurate and ideally will measure the level of antibodies in the bloodstream quantitatively. Such tests are in development, and we will let our members know as soon as they’re available.
What’s One Medical's approach to antibody testing?
One Medical has started accepting patient requests for COVID-19 antibody testing. We are leveraging our existing relationships with commercial labs to analyze patients’ blood samples for the presence of IgM and/or IgG antibodies to the SARS-CoV-2 coronavirus.
Antibody testing is available in all markets where One Medical has a physical presence (San Francisco, Los Angeles, San Diego, Seattle, Portland, Phoenix, Chicago, Washington, DC, Boston and New York.) We strongly recommend our members reach out to our virtual care team through the “Treat Me Now” app to decide which test(s) to order. After connecting with our virtual care team, a provider will guide members to one of our labs to have their blood drawn. Turnaround times for test results are typically a few days, and results are delivered to our members electronically through our app along with guidance from our providers. This guidance is important in helping members more accurately interpret the results of their test. Properly understanding antibody test results is crucial to keeping our patients and others safe, and limiting further spread of the outbreak.
While One Medical’s lab partners are currently using qualitative ELISA tests, we are continuously evaluating other antibody test solutions including quantitative ELISA tests and lateral flow immunochemical tests, and plan to make both of these available to our members in the near future. Quantitative ELISA may prove to be important for determining immunity to COVID-19, and lateral flow tests have the advantage of being conducted in-office within minutes, rather than processed at a specialized offsite lab.
One Medical has a dedicated team constantly evaluating the accuracy, speed, FDA approval status, availability and cost of antibody testing options. We will continue to provide updates to you and to our members as additional testing solutions have been properly clinically evaluated, vetted and approved for use.
The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, Portland, the San Francisco Bay Area, Seattle, and Washington, DC.
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