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Using Prenatal Blood Samples to Evaluate COVID-19 Rapid Serologic Tests Specificity
Jackeline Alger1,2,3,4, Maria Luisa Cafferata5,6, Tito Alvarado1,3
1Plataforma Todos Contra el COVID-19, Tegucigalpa, Honduras.
Insights
COVID-19 rapid tests show varying specificity. Evaluating these diagnostic tests using pre-pandemic blood samples from pregnant women is crucial for accurate results.
Area of Science:
- Infectious Diseases
- Immunology
- Public Health
Background:
- Cross-reactivity in COVID-19 serologic tests can impact specificity.
- Prenatal care offers a unique population for validating diagnostic tests.
- Pre-pandemic serum samples are ideal for assessing test specificity.
Purpose of the Study:
- To evaluate the specificity of COVID-19 rapid serologic diagnostic tests.
- To determine the reliability of these tests using a well-defined sample population.
Main Methods:
- Utilized stored serum samples from pregnant women (collected in 2018).
- Evaluated four lateral flow rapid diagnostic tests for COVID-19.
- Employed blinded evaluators to read test results from pre-pandemic samples.
Main Results:
- Two tests demonstrated 100% specificity for both IgM and IgG antibodies.
- One test showed 98.9% specificity for IgM and 94.4% for IgG.
- Another test yielded 88.9% specificity for IgM and 100% for IgG.
Conclusions:
- COVID-19 serologic rapid tests exhibit variable specificity.
- Sentinel prenatal clinics are valuable for obtaining population-based samples for test validation.
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.
