Studies have shown time and time again that lateral flow tests are only accurate in diagnosing coronavirus when they are performed by trained professionals.
The tests, which give results in less than 15 minutes, use swabs from the nose or throat. The samples are then mixed in a test liquid and placed in a plastic strip that can detect the presence or absence of the 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 the NHS are directing people to use the tests on themselves, although manufacturers of some tools say they should not be used as DIY wipes.
Both the scanning procedure and the use of the test cassette can be easily performed incorrectly and affect the accuracy of the test.
If the swab isn’t done long enough, or deep enough in the nose or throat, it may not pick up bits of the virus. Medical professionals can also use nasopharyngeal swabs, which go directly into the back of the nostril, while this is not recommended for people who test themselves.
If the sample is not properly inserted into the cassette, the result may be wrong, or people may misread the screen when it produces a result.
Precision self-test cutting from 79% to 58%
An evaluation by the University of Oxford and Public Health England found the Innova side-flow test, which is widely used in the UK, that its sensitivity – the percentage of positive cases it discovered – dropped from 79 percent to 58 percent when using it. By untrained members of the public rather than laboratory experts.
Based on this evaluation, officials pushed ahead and used it in a real-world self-exam experience.
The pilot in Liverpool is found to be less than half positive
When the same Innova test was tested on members of the public in Liverpool – with people taking their swabs and training military personnel to run the tests – the swabs picked up only 41 percent of the positive cases.
In the study, rapid tests revealed 891 positive results, compared to laboratory polymerase chain reaction swabs that found 2,829 positive results in the same group. This means that 1,938 people got a false negative from the rapid test.
The study did not compare this to rapid, professionally conducted tests, but the manufacturer Innova claims its test is 95 percent sensitive in laboratory conditions.
… but the test conducted by doctors in Slovakia is ‘low infection’
Although rapid lateral flow tests have become a bad press, officials in Slovakia used them on 5.2 million people – roughly 5.5 million people – in an experiment that a study later estimated had reduced the country’s infection rate by 60 percent.
The tests used were between 70 and 90 percent accurate, and all swabs and evaluations were performed by trained medical personnel. They used swabs from the deep nasopharynx, which go to the back of the nose, while the self-test is generally based on a swab from the nostril only.
Researchers from the London School of Hygiene and Tropical Medicine said the scheme succeeded in eliminating cases of coronavirus that otherwise could not be detected, cutting the number of cases by more than half in a week during the lockdown.
How are the rapid tests different from laboratory-based PCR tests
Lateral flow tests are an alternative to the gold standard PCR test – scientifically known as the polymerase chain reaction test – which is more expensive, more labor-intensive, but more accurate.
PCR tests also use a swab but are then processed using high-tech laboratory equipment to analyze the genetic sequence of the sample to see if any of them match the genes of the Coronavirus.
This is a very long and expensive process, involving multiple types of trained personnel, and the analysis process can take hours, as the whole process from a swab to a person receiving results takes days.
However, it is significantly more accurate. Under ideal conditions, the tests are nearly 100 percent accurate in detecting the virus, although this could be more than 70 percent in the real world.