Covid tests: how can people be positive on lateral flow and negative on PCRs?

Anna Brading with her son, who repeatedly tested positive using lateral flow tests, only to go on and test negative with PCRs. Photograph: David Levene/The Guardian

Lateral flow tests (LFTs) are an increasing part of our everyday lives. But for some individuals, a persistent clash with their PCR test results is undermining their confidence in the system.

The Guardian has been contacted by hundreds of people who have repeatedly tested positive on lateral flow devices (LFDs), but whose confirmatory PCR tests have been relentlessly negative.