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 the most comprehensive review of its kind of Covid-19 testing, researchers have examined all available test accuracy evidence for antibody tests published up to the end of April. They found a total of 54 relevant studies reporting test results for almost 16,000 samples.
Through the antibody tests, the presence of the antibodies immunoglobulin M (IgM) and immunoglobulin G (IgG) can be detected.
Dr. Edward McCutcheon, chief medical officer at MUSC Health-Lancaster Medical Center, said the serological antibody test helps more accurately estimate how much of the population has been exposed to COVID-19, even if they were asymptomatic.
Antibody testing is for patients who believe they may have had COVID-19 in the past, who are not now experiencing symptoms of COVID-19, and who are at least 5 years old.
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".
"Our antibody testing can not differentiate between IgM or IgG, but it will tell you that you have this antibody". Little data were available beyond 35 days. There were not enough data to compare the accuracy of different tests.
A PHE spokesperson said: "Our evaluations have been completed in record time using the samples and tests that were available to us".
The researchers looked for reported results of antibody tests in groups of people known to have had COVID-19, as well as others known not to have had COVID-19. They found that all tests showed low sensitivity (the ability to detect disease) during the first week after symptoms (detecting less than 30% of cases of disease), rising in the second week and reaching their highest values in the third week. But research by pediatricians in Britain concluded that if medical care is delayed - particularly when a child appears seriously ill - "the unintended consequences of the lockdown will do more harm and claim more children's lives than COVID-19". While these first COVID-19 antibody tests show potential, particularly when used two or three weeks after the onset of symptoms, the data are almost 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.
Professor Jon Deeks, Professor of Biostatistics and head of the Test Evaluation Research Group at the University of Birmingham, explains: "We've analyzed all available data from around the globe - discovering clear patterns telling us that timing is vital in using these tests". Cochrane, a British-based journal that reviews research evidence, looked at 54 studies that sought to measure the reliability of the antibody blood tests. "In seroprevalence studies, you're looking beyond that and really we need some data which says, 'How well do they work at three months, four months, five months'".
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 their not-yet-peer-reviewed paper posted on Friday on medRxiv, the researchers also said they found the virus in Barcelona wastewater from January 15 of this year, 41 days before the first case was officially reported there. Most insurance policies cover the test, which involves drawing a blood sample, with a $20 copay.
"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.