I've heard that some UK labs have poor handling leading to cross contamination. Also how many cycles before a positive is detected?
I've heard that some UK labs have poor handling leading to cross contamination. Also how many cycles before a positive is detected?
Some of the lighthouse lab handling is pretty terrible. Plenty of evidence of leaking tubes, cross contamination (and likely staff infection).
cT varies as we use different assays and different machines. Some run all the way to end point, some dont.
FOIA requests showed 40 or so which is pretty normal.
The obvious conclusion is that fears about the impact of false positives on covid statistics has been hugely inflated in some places.
Such as this website.
PCR cant amplify what isn't there.
ok that works - kind of -- no amplification errors but still some "machine errors" / other corona cross reaction errors --- most (all?) of which are eliminated on retesting / deeper testing - and this all happens before an interim or final result is formally published to the patient and their clinician ---- - so the effective false positive rate for the testing process in an area of zero incidence is effectively zero ?
still seems unlikely - obviously we need a better idea what happens in the labs - i think some of the concerns around amplifying the influence of false positives in areas of low (not no) prevelance have come from people with a Pathology Lab Background - but yeas getting back to the IOM or WA you c ant amplify zero?
A 2nd test (ideally with a resample but not always) makes a massive difference in reducing any false positives. in low prevelance.
Ultimately if the viral load is high its unlikely to be a false reading provided your test controls all indicate OK.
IF its borderline you retest (as per UK and WHO guidance).
So yes there are false positives but there are mitigation measures.
The main issue with PCR is it cant distinguish between infected v exposed. Thats a different thing again and isn't a "false positive" as such.
This might be more of an issue the higher the prevalence is as more people will be exposed to viral fragments even if not infected.
We still don't have a reliable, accurate test for detecting *infection*.
