Naked Science Forum

Life Sciences => Physiology & Medicine => COVID-19 => Topic started by: FuzzyUK on 03/02/2021 20:33:06

Title: PCR test - CT value
Post by: FuzzyUK on 03/02/2021 20:33:06

I understand high CT values can give false results in the PCR test so why is the a CT value of 45 specified by the NHS. See page 22 Appendix 5

https://www.ibms.org/resources/documents/guidance-and-standard-operating-procedure-covid-19-virus/guidance-and-sop-covid-19-virus-testing-in-nhs-laboratories-v1-16-march.pdf

Title: Re: PCR test - CT value
Post by: alancalverd on 03/02/2021 23:26:58

Presumably to minimise the incidence of false negatives.

Title: Re: PCR test - CT value
Post by: set fair on 04/02/2021 16:14:47

The corollary is also true, a high Ct value will give more false positives, particularly after the infection has cleared but also among uninfected people. Some virologists say that a positive with a Ct value over 40 doesn't mean much.

Title: Re: PCR test - CT value
Post by: alancalverd on 04/02/2021 21:50:13

True, but given that any treatment will only be symptomatic (apart from injecting embalming fluid into the veins of Trumpists), a high false positive rate is not a problem - what is important in controlling the spread of an epidemic is avoidance of false negatives.