Thread by @nigeltwitt

Any debate about use of rapid antigen tests for screening well asymptomatic individuals for #SARCoV2 needs to acknowledge:

PCR may be more sensitive than LFTs BUT:

1. PCR is costly so not feasible for frequent testing of well asymptomatic except in wealthiest of settings

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2. Inevitable delay in receiving PCR result means infected pass on virus in interim

3. Superior sensitivity of PCR is a disadvantage when detects low levels of virus that aren't transmissible or non-viable virus long after infection

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Rapid antigen tests might miss some cases BUT

4. Lateral flow tests are sufficiently cheap to enable large proportion of the population to be screened frequently (even daily)

5. LFT result within minutes means infectious do not spread virus whilst waiting for result

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6. LFTs perform best in the most infectious

7. LFTs are a ‘red light’ test: positive test = isolate; negative test = continue regular precautions (not a ‘green light’ test to rule out infection)

8. Current ‘red light’ test (temperature measurement) is far inferior

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9. Arguments that negative LFT result might falsely reassure underestimates potential for widespread education about use of ‘red light’ tests

10. Rapid antigen tests are not proposed to replace PCR for diagnosis of symptomatic

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