COVID SCIENCE UPDATE

Some COVID-19 antibody tests are more reliable than others - study

Some COVID-19 antibody tests are much more reliable than others. But even with the best ones, reliability varies among patient subgroups, a new study suggests.

Some tests look for IgM or IgA antibodies, the first antibodies produced by the immune system in response to an invader, which do not remain long in the body.

Other tests - the most common kind - look for IgG antibodies, which generally develop within seven to 10 days after symptoms begin and remain in the blood for some time after the patient recovers.

In a study posted on medRxiv on Wednesday in advance of peer review, researchers analyzed data from 11,809 individuals whose COVID-19 had been diagnosed with highly rated tests to see how well the various antibody assays would "recall" that the patient had been infected.

The most commonly used assays, which look for IgG, had a 91.2% recall rate.

But the IgA and IgM assays had estimated recall rates of 20.6% and 27.3%, respectively, coauthor Natalie Sheils of UnitedHealth Group told Reuters.

"Recall varies significantly across subpopulations and according to timing of the tests, with performance becoming relatively stable after day 14," she said. "The tests performed better for men versus women, for non-whites versus whites and for individuals above age 45." More research is needed to understand why these variations occur, Sheils added. -- Reuters