Used properly, "rapid antigen" COVID-19 tests that give fast results are generally reliable, a new study suggests. The tests have "good" sensitivity, or the ability to correctly identify patients who are infected with the coronavirus, and "excellent" specificity, or the ability to correctly identify people who are not infected, UK researchers reported in The Lancet Microbe.

Unlike gold-standard PCR tests, which involve complex lab equipment and highly trained staff, rapid antigen tests can be processed on the spot.

The researchers evaluated six commercially available tests. Compared to PCR, their accuracy at diagnosing infection varied from 65% to 89% and rose above 90% in patients with high viral loads.

The researchers warn that correct use of the tests is essential, which may happen less often with members of the public than when administered by trained healthcare workers.

Although PCR-based testing is more accurate, they conclude, the rapid tests' "versatility in terms of cost and portability," and their usefulness in disrupting transmission from infected asymptomatic individuals who would otherwise go undetected "could outweigh the risk of missing positive cases."