April 20, 2020
Area(s) of Interest: Public Health
The California COVID-19 Testing Task Force has published evaluation criteria for COVID-19 serology screening—both rapid disposable serology tests and enzyme linked immunosorbent assays.
Rapid Disposable Serology Tests
The market is flooded with commercially available rapid disposable serology tests that resemble home pregnancy tests. The technology is a lateral flow immunoassay performed on a finger-stick blood sample. They are of uncertain reliability and not recommended for individual use since the results – whether positive or negative – are inconclusive. Since the FDA did not require emergency use authorization, many of these disposable tests have not been fully validated and the performance characteristics are not well established.
It’s critically important to know that:
- A positive result does not indicate protection from future COVID-19 infections and does not definitively indicate prior exposure to COVID-19.
- A negative result does not exclude either current or prior COVID-19 infection.
If someone has undergone a rapid serology test, the taskforce recommends the following steps:
For positive rapid serology test:
- Consider obtaining a nasopharyngeal swab for molecular testing to evaluate for the possibility of an active COVID-19 infection;
- Consider sending blood for a COVID-19 serology test performed at a CLIA-certified high complexity clinical lab.
For negative rapid serology test:
- If the individual is symptomatic, consider obtaining a nasopharyngeal swab for molecular testing to evaluate for the possibility of an active COVID-19 infection;
- If the individual is asymptomatic, no further evaluation is indicated.
With so many questions outstanding on the effectiveness in rapid serology tests, the COVID-19 Testing Task Force is urging local public health and government officials to discuss options before deploying mass rapid serology testing.
ELISA Serology Tests
Enzyme linked immunosorbent assays (ELISA) tests are performed on a blood draw sample and performed in high-complexity clinical laboratories. It is important to select a serology test that has been fully validated using plasma or serum from confirmed COVID-19 infected individuals or well-characterized reference samples. Fully validated serology tests are currently offered by a small handful of labs but will soon become more widely available.
- The presence of IgM, IgG, and/or IgA antibodies indicates an immune response to COVID-19 but it is not known at this time if the response is protective against future infections.
- False positive results are possible in serology assays; it is unclear what rate of false positive results will occur in individuals with recent infection by other kinds of coronaviruses, or other inflammatory conditions. Additionally, IgM and IgA antibodies are less specific than IgG.
- The current serology tests do not specifically identify neutralizing antibodies against SARS-CoV-2. Future tests may have this capability. Please refer to the assay manufacturer for details.
- The absence of IgM, IgG or IgA antibodies does not exclude COVID-19 infection. It can take 1-2 weeks after onset of symptoms for antibodies to develop.
If someone has undergone a serology test, the taskforce recommends the following steps:
For positive serology test:
- Consider obtaining a nasopharyngeal swab for molecular testing to evaluate for the possibility of an active COVID-19 infection.
- If IgM only is positive, consider repeat serology in 2-3 weeks to evaluate for IgG which is more specific.
For negative serology test:
- If the individual is symptomatic, obtain a nasopharyngeal swab for molecular testing to evaluate for the possibility of an active COVID-19 infection;
- If the individual is asymptomatic, consider repeat serology in 1-2 weeks.
For more information, see the taskforce’s Evaluation Criteria for COVID-19 Serology Screening