COVID-19 antibody tests -- at least, those on the market through April -- had a window for accuracy of only a few weeks after symptom onset, and little reliable data beyond that point, a Cochrane review found.
In a review of 54 available studies through the end of April, mostly from China, the accuracy of pooled results for combination immunoglobulin (Ig)G/IgM tests was 91.4% (95% CI 87.0-96.6) for 15-21 days post-symptom onset, reported Jonathan Deeks, PhD, of the University of Birmingham in the U.K., and colleagues.
While pooled sensitivity was 96.0% (95% CI 90.6-98.3) for 21-35 days after symptoms, the authors emphasized that estimates of accuracy beyond 3 weeks were based on smaller sample sizes. They also found insufficient studies to identify sensitivity of tests beyond 35 days of symptom onset, according to a review published in the Cochrane Library.
Researchers have been grappling with the question of how to use antibody tests in COVID-19, and what they actually mean. The National Institute of Allergy and Infectious Diseases (NIAID) recently published a review of a workshop conducted in May, which reiterated that serology testing should not be a stand-alone clinical decision-making tool, and that more research is needed about what a positive antibody test means in terms of risk for reinfection and immunity.
On June 19, the FDA issued another letter to healthcare providers about serology tests through its MedWatch system, saying, "FDA is not aware of an antibody test that has been validated for diagnosis of SARS-CoV-2 infection." The FDA pointed to the agency's collaboration with the National Cancer Institute to validate commercially available antibody tests.
Deeks and colleagues attempted to examine antibody testing through a literature review, and came up with similar frustrating results, mainly due to the quality of available data.
"While these first COVID-19 antibody tests show potential, particularly when used two or three weeks after the onset of symptoms, the data are nearly all from hospitalized patients, so we don't really know how accurately they identify COVID-19 in people with mild or no symptoms, or tested more than five weeks after symptoms started," said Deeks in a statement.
Deeks and colleagues noted that half the data were from preprints that had yet to be peer-reviewed. In addition, the studies were small and did not report their results fully or included multiple samples from the same patients.
Moreover, the group noted concerns of risk of bias and applicability. Most studies were in hospitalized patients, and in nearly all cases, the index test was unblinded. There were no studies in exclusively asymptomatic patients.
"The design, execution, and reporting of studies of the accuracy of COVID-19 tests requires considerable improvement," said co-author Jac Dinnes, PhD, also of the University of Birmingham, in a statement.
The authors noted that the main results of the review are from 38 study cohorts out of 54 that stratified results by time since symptom onset. Results were taken from 27 tests out of 200 available tests on the market.
Not surprisingly, pooled results from IgA, IgG, and IgM tests found that sensitivity was less than 30% in the first week, with similar results for combination IgG/IgM. Sensitivity rose to 72.2% (95% CI 63.5-79.5) for 8-14 days and reached 91% at 15-21 days.
The authors questioned the role of antibody testing in serosurveys for public health purposes, saying, "high risk of bias and applicability make it likely that the accuracy of tests when used in clinical care will be lower than reported in the included studies."
Indeed, the researchers estimated that if 1,000 people were administered antibody tests 3 weeks after symptoms started, 5% of whom actually had COVID-19, as is typical in a national survey, 21% would be false positives and 0.4% would be false negatives. In a high-risk setting, like a healthcare facility, where 50% of symptomatic people had COVID-19, the false-positive rate would drop to 2% and the false-negative rate would rise to 8%.
Because the researchers were able to obtain results only from a handful of tests, they said they planned ongoing updates, as this is a "fast-moving field."
Last Updated June 26, 2020
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Disclosures
The authors noted that the paper presents independent research supported by the National Institute for Health Research (NIHR) Birmingham Biomedical Research Centre at the University Hospitals Birmingham NHS Foundation Trust and the University of Birmingham, and that the views expressed are those of the authors and not necessarily those of the National Health Service, the NIHR, or the Department of Health and Social Care.
Deeks is a U.K. National Institute for Health Research Senior Investigator Emeritus and is supported by the NIHR Birmingham Biomedical Research Centre; other co-authors are supported by an NIHR post-doctoral fellowship and the NIHR Birmingham Biomedical Research Centre.
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