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

Abstract

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.

Keywords: COVID-19 diagnostic testing; Pregnancy; Prenatal care; Serologic tests.

Fig. 1

a–c Digital picture of COVID-19 rapid serological test (RDT#1) with negative result (a) and RDT#3 with IgG (b) and RDT#4 with IgM (c) positive results