Thread by @michaelmina_lab

Terrific write up!

Perhaps the most thorough reporting I’ve seen on the controversies surrounding rapid tests

An extremely important point @GiorgiaWithAnI covered is one at heart of the confusion but previously not covered well..

See short thread

1/x

nature.com/articles/d4158…

I’ve spoken on sensitivity and why rapid Ag tests shouldn’t be compared to PCR

Nevertheless, we’re stuck comparing to PCR. So, to deal w this, “we” have taken to comparing rapid antigen tests to PCR results below specific Ct values that may represent contagious virus loads

2/x

In many studies, Ct of <30 or <25 are considered to be likely contagious or “high virus”, respectively

HOWEVER this is bad. We must stop assuming this

Not all labs are the same

A Ct 25 in many labs may = a Ct of 18 elsewhere

This happened in Liverpool w Innova evaluation

3/x

In Liverpool, one scientist made a huge deal of saying that Innova was not performing well at a Ct of 25 - which he considered as “high” virus load.

But it turns out that that lab uses a particularly efficient PCR assay and a 25 is actually “low”. In that lab <18 is “high”

4/x

When evaluated against the correct cutoff for moderate/high virus load (likely contagious virus) the Innova test performed extremely well (>90% overall sensitivity in that range).

So it is SO important for scientists to take the variation in CT values across labs seriously

5/x

The simple failure to accurately translate Ct values to viral RNA load has unfortunately led governments to question certain rapid tests & delay rapid Ag test use... all bc a scientist made a mistake and went to the media before correcting that mistake

(Still hasn’t)

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Thanks @GiorgiaWithAnI for doing such a thorough reporting on the myriad issues of rapid tests. Wonderful write up (see top of thread 👆)

It covers much of the controversy. The issue I discuss here starts halfway down at: “But differently calibrated PCR systems...”

7/7