I remember hearing from what I thought was multiple sources that your run-of-the-mill PCR test had something like a 50-80% sensitivity, and therefore a pretty bad bayes factor for negative tests. But that doesnt seem to square with these results—any idea what Im thinking of?
I think a lot of these numbers are unfortunately sensitive to various conditions and assumptions, and PCR has been taken as the “gold standard” in many ways, which means that PCR is often being compared against just another PCR.
My impression was that, when properly performed, RT-PCR should be exquisitely sensitive to RNA in the sample, but that doesn’t help if the sample doesn’t have any RNA in it (e.g. when someone is very newly infected.) I had assumed that’s where the discrepancy comes from. But then in googling for the limit of sensitivity, I found this: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7302192/ assessing different PCR tests against each other. The best had a “limit of detection” of 100 copies of RNA per mL of sample. But apparently there is a LOT of variation between commercially-available PCR tests. :-(
I remember hearing from what I thought was multiple sources that your run-of-the-mill PCR test had something like a 50-80% sensitivity, and therefore a pretty bad bayes factor for negative tests. But that doesnt seem to square with these results—any idea what Im thinking of?
I remember something like what you’re talking about, I think—googling finds e.g. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0251661 making this case.
I think a lot of these numbers are unfortunately sensitive to various conditions and assumptions, and PCR has been taken as the “gold standard” in many ways, which means that PCR is often being compared against just another PCR.
My impression was that, when properly performed, RT-PCR should be exquisitely sensitive to RNA in the sample, but that doesn’t help if the sample doesn’t have any RNA in it (e.g. when someone is very newly infected.) I had assumed that’s where the discrepancy comes from. But then in googling for the limit of sensitivity, I found this: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7302192/ assessing different PCR tests against each other. The best had a “limit of detection” of 100 copies of RNA per mL of sample. But apparently there is a LOT of variation between commercially-available PCR tests. :-(