Off-the-shelf medical tests that promise to diagnose conditions ranging from vitamin deficiencies to cancer are lacking evidence to back up their accuracy, a study has found.

Thirty self-testing kits were purchased from a range of mainstream supermarkets, pharmacies and health and wellbeing shops by researchers from the University of Birmingham in 2023.

The kits tested for vitamin deficiency, blood cholesterol, menopause and bowel cancer. These tests are often marketed as tools for empowerment and early detection at a time when the NHS is already over-stretched.

Accuracy claims were made for 24 of these tests however, and nearly six out of 10 (14) promised 98% accuracy. However, evidence supporting these claims was largely unavailable, according to a series of papers published by the British Medical Journal (BMJ).

In addition, 18 of the tests (60%) were found to have errors that could lead to a wrong result. This included 11 that had problems with equipment, 10 showing issues with the sampling process and 15 that had problems with the instructions of interpretation of results.

Where information about what types of accuracy methods were available, about a third of those compared their test with another similar test – not a proper, trusted medical test.

Most of the tests also did not explain who they tested them on to provide the accuracy data.

These types of testing kits are not subject to the same stringent checks that a new medication would have to go through.

The University of Birmingham’s Professor Jon Deeks, a corresponding author of the study, said: “Our findings highlight concerns about the value of these self-tests because the instructions for use for many of them recommended seeing a doctor regardless of the test result (positive or negative).”

Can these tests cause harm?

Dr Clare Davenport, co-author of the study, said the benefit of many of these tests “is lacking”.

“This is in contrast to well-established self-tests, such as pregnancy tests,” she said.

“We are worried that consumers concerned about their health and tempted by the convenience of buying a test over the counter may be harmed if they use these tests in the wrong way.”

A false positive on such a test may lead to anxiety, unnecessary investigations and even overtreatment, while a false negative could lead to delays in treatment.

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Image:
Pic: University of Birmingham

Researchers are now calling for better regulation and guidance from manufacturers, retailers and healthcare professionals to protect consumers of off-the-shelf health self-tests.

There were some limitations to the test – namely that they were bought two years ago and were not intended to be a sample of what is available across the country.

“But given what they do say about where they got the tests, I’d be surprised if they aren’t pretty much the same anywhere nowadays,” said Professor Kevin McConway, emeritus professor of applied statistics at The Open University.

He said the results were “scary and concerning”.

“I don’t doubt the findings of the researchers, that many of the available tests don’t make it clear who could make good use of them, how accurate the results might be, or what someone should do in the light of their results.”

‘History offers cautionary tales’

“Self-tests should not be dismissed outright though,” wrote Jessica Watson from the Centre for Academic Primary Care, and Margaret McCartney, from the University of St Andrews, in an editorial for the BMJ.

“History offers cautionary tales: when home pregnancy tests were first introduced, some doctors argued that women could not be trusted to use them.

“Clearly that is not the case.

“The use of HIV self-tests has been extensively and carefully evaluated, with decades of research, including large randomised controlled trials.”

However, they say that these examples are of tests that are “binary” with yes or no answers, and are integrated within healthcare systems, “with clear actions to be taken based on the results”.

The study was funded by the National Institute for Health and Care Research (NIHR) Birmingham Biomedical Research Centre.