A first-of-its-kind study published today in AACC’s Clinical Chemistry journal compared the performance of two COVID-19 antibody tests and found that—even though both tests are FDA authorized—one produced more incorrect results than the other. These findings could help healthcare professionals and researchers to better select antibody tests, which are essential to both treating COVID-19 patients and determining the full extent of the outbreak.

COVID-19 antibody tests play a vital role in identifying people who have recovered from the virus and who have high levels of antibodies in their blood that could potentially help other critically ill COVID-19 patients. Antibody tests are also essential to population screening efforts that aim to find out how widespread the virus really is. Many reports have emerged, however, of antibody tests on the market that are of dubious quality. This is partly due to the fact that, in response to concerns that FDA regulation was hindering COVID-19 testing, the agency temporarily allowed diagnostic manufacturers to sell antibody tests without undergoing FDA review. The agency has since revised this stance, and now requires manufacturers to apply for emergency use authorization within 10 days of releasing an antibody test. However, due to the high demand for COVID-19 tests, even some FDA-authorized antibody tests have undergone abbreviated validations. For example, one company that received FDA authorization evaluated its antibody test on only 8 patients, even though at least 50 patients with confirmed disease should be used for these types of test validations.

To fill this validation gap, a team of lab experts led by Christopher W. Farnsworth, PhD, from the Washington University School of Medicine in St. Louis, compared the performance of two COVID-19 antibody tests that have received FDA authorization: the Abbott SARS-CoV-2 IgG and the Euroimmun Anti-SARS-CoV-2 ELISA (IgG). With these tests, the researchers analyzed 103 specimens from patients with COVID-19 infections diagnosed using standard molecular testing and 153 specimens from healthy individuals. From this, the researchers found that Abbott’s test had a specificity of 99.4% and a sensitivity of 93.8% at ≥14 days after symptom onset, while Euroimmun’s test had a specificity of 94.8% and a sensitivity of 85.4% at ≥14 days after symptom onset.

Overall, the Abbott test’s high sensitivity and specificity mean that it produces fewer inaccurate results than Euroimmun’s test. However, it’s worth noting that the 93.8% sensitivity that the researchers found for this test is actually lower than the 100% sensitivity that the company states its test exhibits. A possible explanation for this discrepancy is that the test subjects Abbott used were likely patients who had fully recovered from COVID-19, while Farnsworth’s study included hospitalized patients.

“This demonstrates the importance of testing patients who have fully recovered from infection and hospitalized patients with multiple comorbidities including immunodeficiencies,” said Farnsworth. This finding also underscores the point that, “given the relaxed regulatory requirements by the FDA on SARS-CoV-2 serology tests, it is crucial for clinical laboratories to uphold the rigor of assay validation and to determine if assay performances, as reported in package inserts, are accurate.”

The study can be read here:https://academic.oup.com/clinchem/advance-article/doi/10.1093/clinchem/hvaa120/5836557