Statement
Concerns have been raised about the Government’s mass testing strategy (see: Are PCR tests fit for purpose?). Even after the huge investments of the past year and high hopes in the field, there are still fundamental questions about the basic efficacy of some of the take-at-home testsPCR testing and the accuracy of lateral flow device (LFD) tests, also known as antigen tests.
In March 2021, a systematic review was published in the Cochraine Library’s Database of Systematic Reviews (systematic reviews are used, particularly in health research, to identify, evaluate and synthesise all the empirical evidence that meets pre-specified inclusion criteria to answer a specific research question).
The review reported that “in people with confirmed Covid‐19, antigen tests correctly identified Covid‐19 infection in an average of 72% of people with symptoms, compared to 58% of people without symptoms. Tests were most accurate when used in the first week after symptoms first developed ….”
A government evaluation, in association with Oxford University, found that the ability of the LFD test to correctly identify those without Covid-19 (called ‘true negatives’). It found the lateral flow tests have a specificity of at least 99.9% (fewer than one false positive in every 1,000 lateral flow tests).
The analysis of the data, however, has been critiqued by some biostatistics experts who said that “when disease prevalence drops, even the most specific tests face problems as the number of false positives can outnumber the number of true positives – a scenario where a confirmatory test is absolutely essential to prevent large numbers being made to unnecessarily isolate.” The Government has since reversed the policy.
“We’re in this ridiculous state where people are being invited to test themselves twice a week with a test that’s really unreliable,” says Will Irving, professor of virology at Nottingham university, referring to the lateral flow devices. “If you get a negative result it doesn’t mean you haven’t got it, if you get a positive result, it doesn’t mean you’ve got it.”