COVID-19 Impact Bulletin: Testing 101

There are two main types of COVID-19 tests:

• a viral test, which determines a current infection and
• an antibody test, which determines a prior infection.

COVID-19 Viral Testing: Viral tests check samples from the respiratory system (taken by swabbing the nose or mouth) to determine if the SARS-CoV-2 virus is present. Two types of diagnostic tests are used to determine if a patient has an active infection: Molecular and Antigen. Molecular tests look for genetic material created by the virus, while the antigen tests look for specific proteins created by the virus.¹ Antigen tests usually provide faster results but have a higher probability of missing an active infection, according to the FDA. A Harvard Medical School study found that the false-negative rate of an antigen test is as high as 50%, while the false-negative rate for a molecular test ranges from 2% to 37%. A false negative means the test determined that a person was not infected, when in fact they were. The false-positive rate is near zero for both tests.² As a point of comparison, the rapid influenza test which is used to test for seasonal influenza, has a false-negative rate of 50%-70%, which means it fails to identify the presence of influenza at least half of the time. Like the COVID-19 test, the false-positive rates for common influenza testing are very low.³

COVID-19 Antibody Testing: The COVID-19 antibody (serology) tests determine if a person has recovered from a COVID-19 infection. It takes an infected person 1-3 weeks to begin producing antibodies, so the test will neither identify an active COVID-19 infection nor detect a very recent infection. The blood test screens for antibody proteins that would have been developed by the patient to fight off COVID-19 and provide protection against re-infection for a still unknown period of time.¹ The Harvard Medical School study determined the results could be skewed if the test is taken too soon after an infection. The current estimate of false negatives for COVID-19 serology tests is estimated to be around 20%.²

The FDA has compiled a comparison chart providing an overview of COVID-19 tests: