Using prenatal blood samples to validate COVID-19 rapid serologic tests

Abstract

IntroductionBackground cross-reactivity with other coronaviruses may reduce the specificity of COVID-19 rapid serologic tests. Blood collected during prenatal care is a unique source of population-based 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. MethodsWe randomly selected 120 stored serum samples from pregnant women enrolled in a cohort in 2018, at least one 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. The third test had a specificity of 98.9% for IgM and 94.4% for IgG. The fourth test had a specificity of 88.9% for IgM and 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.

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“…• Agreement of 100% among laboratory scientists, four products (45) • Agreement between trained evaluators 95.3% (91) • Agreement between lay volunteers (home-testing) and health professionals (92)…”

“…• Proportions of invalid test results were assessed in 6 studies for 20 products • For four products-all assessed on plasma and serum, proportions of invalid tests were 0-0.1% (27,86,90,91). • For 11 products assessed on EDTA-anticoagulated venous blood (32), invalid or inconclusive results were absent or very low (<1%) for eight products, but 16/0, 21.0, and 23.0% the remaining three products, mostly caused by insufficient background clearing (see above) • For two products assessed for self-testing [see above (92)], invalid results were of 4.8 and 7.4%…”

Polymorphism and Selection Pressure of SARS-CoV-2 Vaccine and Diagnostic Antigens: Implications for Immune Evasion and Serologic Diagnostic Performance

“…Such tools will be critical to increase testing for the accurate and rapid identification of cases and their isolation to limit further transmission of the virus. However, their performance needs to be evaluated, and initial testing suggested variable performance of these tests [2,3]. Test performance relies in part on the antigen used, and its conservation among virus strains circulating in the population being tested.…”