Lateral flow tests are only accurate in diagnosing coronavirus when performed by trained professionals, studies have repeatedly shown.
The tests, which provide results in just 15 minutes, use swabs from the nose or throat. Samples are then mixed in a test liquid and placed in a plastic cassette that can detect the presence or absence of coronavirus and then produce an image of a line, in the same way as a pregnancy test, to indicate whether it is positive or negative .
The Department of Health and NHS are instructing people to use the tests on their own, despite manufacturers of some kits saying they should not be used as DIY swabs.
Both the swab procedure and the use of the test cassette can be easily done wrong and affect the accuracy of the test.
If the swab is not done long enough or deep enough in the nose or throat, it may not pick up fragments of the virus. Medical professionals may also use nasopharyngeal swabs, which go up to the back of the nostril, while this is not recommended for people testing themselves.
And if the sample is not properly placed in the cassette, the result may be wrong, or people may misread the display when it returns a result.
SELF-TESTING CUTTING ACCURACY FROM 79% TO 58%
A review by the University of Oxford and Public Health England of the Innova lateral flow test, widely used in the UK, found that its sensitivity – the percentage of positive cases detected – dropped from 79 percent to 58 percent when it was tested. was used by untrained members of the public rather than laboratory experts.
Based on this evaluation, officials went ahead and used it for a real self-test.
PILOT FOUND IN LIVERPOOL LESS THAN HALF THE POSITIVES
When the same Innova test was tried on members of the public in Liverpool — with people taking their own swabs and trained military personnel performing the tests — the swabs picked up only 41 percent of positive cases.
In the study, the rapid tests detected 891 positive results, compared to lab-based PCR swabs that found 2,829 positives in the same group. This means that 1,938 people got a false negative result from the rapid test.
The study did not compare this to professionally performed rapid tests, but the manufacturer Innova claims that its test is 95 percent sensitive under laboratory conditions.
…BUT PERFORMED BY MEDICINE IN SLOVAKIA ‘REDUCED INFECTIONS’
Despite rapid lateral flow tests getting bad press, officials in Slovakia used them on 5.2 million people — nearly the entire population of 5.5 million — in a trial that a study later estimated reduced the country’s infection rate by 60 percent. was reduced.
The tests used were between 70 and 90 percent accurate, and all swabs and evaluations were performed by trained medical professionals. They used deep nasopharyngeal swabs, which go to the back of the nose, while self-tests are generally based on a swab from the nostril only.
Researchers from the London School of Hygiene & Tropical Medicine said the program successfully eradicated coronavirus cases that would not otherwise have been found, cutting cases by more than half in a week during a lockdown.
HOW QUICK TESTS DIFFER FROM LAB-BASED PCR SWABS
Lateral flow tests are an alternative to the gold standard PCR test – scientifically known as polymerase chain reaction testing – which is more expensive and labor intensive, but more accurate.
PCR testing also uses a swab, but this is then processed using high-tech lab equipment to analyze the sample’s genetic sequence to see if it matches the coronavirus genes.
This is a much longer and expensive process, involving multiple types of trained personnel, and the analysis process can take hours, with the whole process from swab to someone receiving their result taking days.
However, it is significantly more accurate. In ideal conditions, the tests are nearly 100 percent accurate in detecting the virus, although in the real world it could be more than 70 percent.