The Royal College of Pathologists (RCPath) recognises the potential role of Lateral Flow Antigen Tests for COVID-19 (LFTAg) 1 when used in a controlled and targeted way as part of an overall testing strategy. However, the public is reminded that the currently-used versions of these tests are not of sufficient sensitivity or accuracy to rule out the possibility that a negative result may not be correct. Whilst a negative FTA result reduces the chance that the person tested is infected, it does not eliminate it; therefore, that person could still potentially infect others.2
Individuals with negative LFTAg results should still observe social distancing and respiratory hygiene precautions (such as face masks covering the nose and mouth) whilst around others.
Positive results by LFTAg should be confirmed by testing in a laboratory (using reverse transcription-polymerase chain reaction testing (RT-PCR)) as a matter of urgency. In the meantime, individuals with a positive LFTAg result should self-isolate pending the confirmatory test result.
1. Lateral Flow Antigen tests are rapid turnaround tests that can process COVID-19 samples on site without the need for laboratory equipment, with most generating results in under half an hour.
2. As the prevalence of infection declines in the population, the test's positive predictive value will also decline, meaning, the proportion of positive results which are false positives will rise. When utilising a test for case finding in asymptomatic people, it is usual to employ a test with high sensitivity in order to detect as many cases as possible, and then to confirm any positive results with a test of high specificity, to avoid false positives and the downstream problems associated with these.