We’ve talked here about the problems and limitations of antibody tests. We’ve seen others discuss it. And a primer on the mathematical whys and wherefores is available here.

Today some pre-publication data on a variety of US antibody tests were released, and they aren’t great–and they illustrate precisely the problems discussed above:

Some key points:

• One test never delivered a false positive; two others were 99% accurate. HOWEVER, no test was better than 80% accurate until 3 weeks post-infection;
• of over 100 tests on the market, 12 were evaluated;
• the wide differences in positive rates (21% in New York to 3% in some areas) suggests that part of the difference is the type of test being used, and their false positive rate (telling people they’ve got antibodies when they really don’t);
• The tests with best results were made by Sure Biotech and Wondfo Biotech;
• Quite a few did 95% or so. But as you remember from our discussion, in a relatively low population rate (15% true positives, which is probably higher than Alberta is right now), 1 in 4 of those will still be a false positive. If we’re lower than that, that number climbs and is even worse;
• “false positives are less of an issue for assessing how widely the virus has spread in the population. If a test has a known false-positive rate, scientists can factor that into their calculations,” he said. But false positives become dangerous when making policy and personal decisions about who can go back to work. “You don’t want anybody back to work who has a false positive — that’s the last thing you want to do,” And, this is precisely why we’d like them–to know who to clear, and we can’t use them for that yet.

Remember that the lower the population rate of true positive, the more false positives become the more likely outcome. (See our review here to understand why if you need a refresher.)

This isn’t peer reviewed yet, so caveats apply. The team that did it has a history in evaluating other such tests for Chagas’ disease, so they know what they’re doing.

You can see the team’s research for yourself here.