CDC Says Possibly 'Less Than Half' Of Positive Antibody Tests Are Correct

forbes ^ | Updated May 26, 2020, 07:56pm EDT | Tommy BeerForbes Staff

[Pearls Before Swine]

If the test yields a false positive 5% of the time, in a population with 5% actual frequency, then it would mean that half of the folks testing positive wouldn’t actually have the disease.

I completely understand that. Have you ever looked at the specs for electrical meters or o-scope displays? The uncertainty is typically expressed as "so many percent of display value PLUS so many percent of full scale."

That pretty much holds with these tests. At low probability levels, the potential error rate ("offset") is high, as the population's positivity rises, the precision of the test increases.

On you second point (extra post): I agree that positives of people in the early stages of infection should be interpreted differently than those of other positives in presuming immunity. But, as the ratio of recoveries compared to infected rise, that becomes less of a consideration. It was a big factor 45 to 60 days ago.

[Toirdhealbheach Beucail]

In the real world of In Vitro Diagnostic Kits and other text kits, a 50% false positive rate would have a rather difficult time being approved by the FDA.

[Pearls Before Swine]

One would hope.

But accelerated approvals, or at least relaxed trial criteria, seem to be the order of the day. And I note that there are examples of hopeful but uncertain therapies today. Take, for example, the annual flu shot.

Regardless, no one is telling us what the accuracy or specificity of the kits used for measurement is... we just get numbers, without an estimate of their range of uncertainty.

Hopefully, that will improve soon.

[Hot Tabasco]

I recently had the antibody test and the results came up negative. My nephew was quite ill with the virus for about two weeks but yet his live in fiance never got sick and she recently tested negative for the antibodies when all logic says she should have contracted the virus.

In the 2017-18 epidemic, there were 48.8 million cases but yet over 280 million people never caught it, including me, despite no shut downs, no social distancing and no masks......

So my humble opinion is that you are either going to catch it or you won't and any actions you make take to try and protect yourself from contracting it are just a useless waste of time........