What’s the value of a confirmatory PCR test? | David Spiegelhalter and Anthony Masters

A positive lateral flow test, followed by a negative PCR, still means a reasonable chance of Covid-19

After a wave of cases in which a positive lateral flow device (LFD) test was followed by a negative PCR test, a private laboratory handling swab tests has been suspended.

But conflicting results are not a new problem. Back in June, when secondary school students with a positive LFD were retested with a PCR check, over one in eight came back negative. And even without laboratory problems, it is unclear why a negative PCR should trump a positive LFD.

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