The FLARE Four
- Accurate SARS-CoV-2 serology will allow diagnosis of previous infection, assessment of seroprevalence and potentially identification of individuals with protective immunity
- Current SARS-CoV-2 serological assays were developed rapidly and vary with regard to their sensitivity and specificity
- The relationship between a positive antibody test result and protection from future SARS-CoV-2 infections requires further study
- The results of an antibody test should not be used to determine infectivity and contagiousness
Small initial studies have demonstrated that most patients infected with SARS-CoV-2 develop antibodies against the virus. The promise and current pitfalls of antibody testing are reviewed in a fast literature update posted on May 22, 2020, by Alison Witkin, MD, associate director, Pulmonary Hypertension and Thromboendarterectomy Program with advisory review by Rod Rahimi, MD, PhD, both of the Department of Pulmonary and Critical Care Medicine at Massachusetts General Hospital.
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Antibody Testing Uses
Antibody testing may be helpful for:
- Identifying the prevalence of SARS-CoV-2 infection in a population, and predicting the future course of the pandemic
- Determining infection status in a patient with a high clinical suspicion for disease who had a negative molecular test
- Identifying potential donors of convalescent plasma
- Assessing response to vaccines under development
- Offering information about prior infection to patients who had COVID-19–like symptoms but had a negative SARS-CoV-2 PCR or could not be tested
Problems with Interpretation
The FDA has made SARS-CoV-2 antibody tests available under emergency use authorization, which facilitates rapid implementation but decreases the rigor of evaluation. To date, the agency has approved 16 tests with sensitivity (true positive rate) of 87%–100% and specificity (true negative rate) of 96%–100%. This variability has important implications for interpretation of results.
For clinicians, the positive and negative predictive values of a test are more informative than sensitivity and specificity. As positive and negative predictive values depend on disease prevalence, well-conducted epidemiological studies with a sensitive and specific serological assay are needed before clinicians can make informed interpretation of individual patient results.
Other Points of Caution
The relationship between any one positive antibody test and protection from future SARS-CoV-2 infections is still unknown. In addition, the results of antibody testing don't imply anything about infectivity and contagiousness—seropositive individuals may nevertheless shed contagious virus and, conversely, seronegativity doesn't rule out acute infection.
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