There are a few different types of tests for COVID-19. Currently the most common is a PCR test, which detects genetic material from the virus. PCR tests are great because they are highly specific - they have a very low rate of false positives. If the test is positive, you can be certain you have COVID-19. But the test only works on patients who are sick and still have the virus in their body. What if you want to know if someone had COVID-19 in the past? That's where antibody tests (also known as serology) comes in.
For more details, keep reading.
There are a handful of situations where antibody tests are useful:
For more details, keep reading.
What good is an antibody test?
There are a handful of situations where antibody tests are useful:
Identification of potential convalescent serum donors
Patients with COVID-19 begin to develop antibodies against the virus 1-2 weeks after symptom onset. Those antibodies can be collected and used as treatment for others who are critically ill from the disease. Antibody testing can verify that a recovered (convalescent) patient has antibodies useful for therapy.
Identification of protective immunity
Patients who recover from COVID-19 probably have immunity against another infection. I say probably -- this hasn't been proven yet, and even if immunity does develop, it's possible that the immunity wears off over time. People who have immunity would be able to move about society without worrying about getting infected or passing the virus to others.
Contact Tracing
Once the number of active cases in the United States decrease, contact tracing will play an important role in preventing another widespread outbreak. If a contact reports a recent illness from which they recovered, antibody testing would help to confirm they had COVID-19. |
Diagram of COVID-19 Tests. Source: American Society for Microbiology
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Do we Have an Antibody Test Yet?
Several articles in the popular press have noted that an antibody test should be available in the united states soon. In reality, many test kits are already available, but issues regarding accuracy and questions about when this sort of test should be used are still being sorted out.
Antibodies in patient blood were first detected by Chinese scientists in February. Since then, numerous groups from China have reported detecting antibodies using variety of similar tests. The accuracy of these tests have been variable, with sensitivity ranging from 48% - 98.6% and specificity ranging from 89% - 99%. Most tests have been done of venous blood (collected by a phlebotomist), though one study used fingerstick blood (similar to how blood for a glucose monitor is checked) and demonstrated that the results using fingerstick blood and venous blood were equivalent (though this was only verified on seven patients). An italian group tried using an antibody test to diagnose COVID-19, and found that it was a poor tool for diagnosing patients.
This Nature Biotechnology article has a list of antibody test kits that have been developed and notes about their approval status; additionally FindDx.org maintains a list of kits that are under development and their current regulatory approval status.
Before these tests can be used, their precise level of accuracy needs to be determined. They will be useful to determine what portion of the population have been exposed to SARS-CoV-2. A clinical trial is underway to begin making this determination.
Do you have questions about Coronavirus? Leave a comment and I'll do my best to answer it, either in a comment or a blog post.
Good informative post. A one-sentence explanation of "sensitivity" vs "specificity" would have been helpful :) but I looked it up easily.
ReplyDeleteHow long do you think it will take for antibody tests to become accurate enough for widespread use?
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