Testing for COVID-19
Updated July 30, 2021
Originally published April 4, 2020
Since the beginning of the pandemic, we've continuously heard about recognizing the symptoms of COVID-19. Besides the symptomatic picture, getting tested for the virus that causes COVID-19, SARS-CoV-2, is key in diagnosing the disease. But with different types of tests available, it can be confusing to ascertain which test will be the most informative.
In an acute care setting such as the hospital or urgent care, there are two tests that are the most useful: PCR and Antigen Testing
PCR Testing
- This test consists of a nasopharyngeal swab and has been available since the inception of the pandemic. It is also the most widely used test in a hospital setting. PCR tests for the presence of genetic material of a virus, and if positive, indicates the presence of viral particles. When correlated with a patient's symptoms and overall clinical picture, positive results are suggestive of an active infection. PCR testing is the most sensitive type of test, and can be positive 4-6 weeks after an infection. This does not mean that all positive PCR tests indicate an active, contagious infection. A positive PCR test after the contagious and symptomatic period has ended merely suggests the continued presence of viral material.
Antigen Testing
- This test consists of a nasopharyngeal swab and has become available over the past few months. Antigen testing is looking for proteins associated with the virus. While not as sensitive as the PCR test, a positive result indicates an active infection with the SARS-CoV-2 virus, as well as being contagious. This test can be used to see if a patient is still contagious, and with improved sensitivity and wider availability, may replace the PCR test.
Outside of the hospital, a third test is also available: Antibody Testing
Antibody Testing
- This test consists of a blood test and has been available for several months. Antibody testing is used to evaluate a patient's immune system recognition of the virus. If positive for IgG and IgM antibodies, it indicates a patient had a previous infection in the past 2-4 weeks. The IgG antibody can be protective against reinfection, however, the timeline of protection is unknown with current estimates at 3-6 months. Nevertheless, antibody testing is primarily useful in large, epidemiological studies to help better understand the disease. As studies examining long-term vaccination efficacy continue to be conducted, antibody testing may be useful in determining an individual patient’s
How do I know what strain of COVID-19 I may have?
- Testing to elucidate the specific strain of COVID-19 requires highly complex genomic testing that is typically only available in large academic and research centers. Your local hospital may not have this testing available. Guidance towards diagnosing the specific strain of COVID-19 is centered around the most prevalent strain circulating in a given area, along with information from national organizations.