Using Prenatal Blood Samples to Evaluate COVID-19 Rapid Serologic Tests Specificity

Introduction Background cross-reactivity with other coronaviruses may reduce the specificity of COVID-19 rapid serologic tests. The vast majority of women attend prenatal care, which is a unique source of population-based blood samples appropriate for validation studies. We used stored 2018 serum samples from an existing pregnancy cohort study to evaluate the specificity of COVID-19 serologic rapid diagnostic tests. Methods We randomly selected 120 stored serum samples from pregnant women enrolled in a cohort in 2018 in Tegucigalpa, Honduras, at least 1 year before the COVID-19 pandemic. We used stored serum to evaluate four lateral flow rapid diagnostic tests, following manufacturers’ instructions. Pictures were taken for all tests and read by two blinded trained evaluators. Results We evaluated 120, 80, 90, and 90 samples, respectively. Specificity for both IgM and IgG was 100% for the first two tests (95% confidence intervals [CI] 97.0–100 and 95.5–100, respectively). The third test had a specificity of 98.9% (95% CI 94.0–100) for IgM and 94.4% (95% CI 87.5–98.2) for IgG. The fourth test had a specificity of 88.9% (95% CI 80.5–94.5) for IgM and 100% (95% CI 96.0–100) for IgG. Discussion COVID-19 serologic rapid tests are of variable specificity. Blood specimens from sentinel prenatal clinics provide an opportunity to validate serologic tests with population-based samples.