Still so much confusion about rapid antigen tests. They get compared to qPCR and bc qPCR is deemed the gold standard, they appear as “low sensitivity”
To be clear, the problem is not the Ag test, it is the v low specificity of qPCR to delineate who needs to be isolated still
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To be clear, the problem is not the Ag test, it is the v low specificity of qPCR to delineate who needs to be isolated still
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https://twitter.com/michaelmina_lab/status/1380541707998138371
qPCR is highly specific as a medical test to appropriately identify SARS-CoV2 RNA....
but qPCR is terribly NOT specific as a public health test to determine who should still be isolating (though looking at Ct values can help)
This is not good for public health.
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but qPCR is terribly NOT specific as a public health test to determine who should still be isolating (though looking at Ct values can help)
This is not good for public health.
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We never should have made qOCR the gold standard for evaluating public health tests. It was a mistake from the beginning bc as CDC readily says - you stay positive on a qPCR test for weeks after you are done transmitting. The specificity is terrible as a public health tool
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At the very least, we should recognize this when evaluating rapid Ag tests bc these tests are highly specific to detect only ppl who are still needing to isolate bc they are infectious.
The tests have different purposes
Remarkable that this conversation still has to happen
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The tests have different purposes
Remarkable that this conversation still has to happen
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It is true that Ag tests are not as sensitive as qPCR. Of course. But that’s always the tradeoff in medicine and public health. When something is too sensitive it often becomes non-specific. And when too specific it is often not as sensitive.
However...
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However...
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The many stories that Ag tests are only 30% or 40% sensitive compared to qPCR in asymptomatic people is driven largely (by a long shot) by qPCR lacking specificity for who needs to isolate, not Ag tests lacking sensitivity for those needing to isolate
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This is readily noted by recognizing that average person needs to isolate for 10 days. Meanwhile qPCR is positive for 20-30 days. It’s simple math.
10 d isolation / 25 days PCR pos = 40%
60% of time that qPCR is positive, we do NOT want or expect Ag test to be pos...
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10 d isolation / 25 days PCR pos = 40%
60% of time that qPCR is positive, we do NOT want or expect Ag test to be pos...
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