Research review shows when COVID-19 antibody tests might be effective
A review of published research on COVID-19 antibody tests show that the tests are most effective at detecting whether someone has had the disease two or more weeks after their symptoms started.
The results highlight that the timing of an antibody test is critical - the tests do not work accurately when administered at the wrong time.
The immune system of people who have COVID-19 responds by developing proteins in the blood called antibodies that attack the virus. Detecting antibodies in people’s blood may indicate whether they currently have COVID-19 or have had it previously.
The researchers, supported by the NIHR Birmingham Biomedical Research Centre, searched through more than 11,000 publications on COVID-19 available at the end of April 2020.
They identified 54 studies from Asia, Europe and the USA that measured the accuracy of antibody tests to detect current or past COVID-19 infection, either in hospitals or the community. In total these studies reported nearly 16,000 test results.
When the researchers pooled all these data, they found that all COVID-19 antibody tests were poor at detecting the disease during the first week after symptom onset (detecting less than 30% of cases of disease). Accuracy rose in the second week and reached its highest value in the third week.
Their new Cochrane review also showed that antibody tests will miss 1 in 10 cases of COVID-19. However the authors caution over reliance on this figure, because the studies included in the review were small, poorly reported and done in select patient groups.
Most of the studies in this review evaluated seriously ill patients in hospital, so the researchers could not determine whether the tests can detect lower antibody levels associated with milder and asymptomatic COVID-19 disease.
Jon Deeks, Professor of Biostatistics and head of the Test Evaluation Research Group at the University of Birmingham and NIHR Senior Investigator Emeritus, said: “Accurate testing is vital – these tests may help identify COVID-19 in people who have had symptoms for two or more weeks but never had a swab test, and in identifying how many have had the SARS-CoV-2 infection to assess disease spread and the need for public health interventions.
“In time, we will learn whether having previously had the infection provides individuals with immunity to future infection, which will indicate the personal value of having this test."