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
Identification of protective immunity
Contact TracingOnce 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
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.