Lateral Flow Test Update
Whilst the success of the vaccination programme and government measures are rightly making headlines, regular testing remains necessary to try and find cases in the community.
Lateral flow tests have been publicly available for some weeks. The aim is to test people who do not have symptoms in order to find hidden cases and break the chain of transmission.
Although the tests have weaknesses, they do have a place in helping to control the virus. This is because they offer quick results and are much cheaper to use than PCR testing.
To date, only limited data has been made available to assess the accuracy of the tests. The “Liverpool” study (which has yet to be peer-reviewed) found a sensitivity of 40%, but it was based on only 78 participants.
A recent Cochrane analysis of 64 different studies found that test sensitivity in symptomatic people ranged from 34% to 88%, with an average of 72%. The performance of the Innova lateral flow test in asymptomatic people was not included in the analysis.
At the end of March Jon Deeks, Professor of Biostatistics at the University of Birmingham and the Cochrane review’s lead author predicted more false positives and fewer true positive results as infection levels fall. Expert committees advising the Health & Safety Executive have reported similar concerns.
The latest data
Now data published by the Department of Health & Social Care has shown the results from the first two weeks of testing in secondary schools using Innova tests.
The results indicate that the tests are indeed finding more false positives than true positives (62% were false positives in the first week). There was 1 positive per roughly 6,900 tests done.
All tests have limits
It is important to balance to the positive effects of the tests with the potential harms that may be caused by using them. This can be a subjective opinion although as more evidence is made available it is becoming easier to have a better informed debate.
Benefits to lateral flow tests
- Rapid results
- Portable kits
- Easy to use
- Less expensive than PCR
Potential risks from lateral flow tests
- Missed cases
- False positives
- False reassurance
The MHRA has expressed concern about the tests being used as ‘green light’ tests i.e. if your result is negative you cannot be certain you are not infectious. This is of importance if people are being tested before coming to work.
Using the tests in workplace settings also places legal obligations on businesses to store tests properly, comply with GDPR sensitive data laws, liaise with Public Health England and report faulty kits to the MHRA. More information is included in our workplace testing guide for employers.
Testing does not replace risk management
Because lateral flow tests have known weaknesses they cannot be a substitute for infection control measures.
If the aim is to break chains of transmission, the simple steps are currently likely to be the most effective for businesses; good hygiene, social distancing, PPE and rapid testing of any symptomatic cases via the NHS.
If infection rates in the community rise again then justification for using lateral flow tests will increase (and the risks will lower), as the likelihood of false-positive results will reduce.
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