Popular screening tests with limited evidence: what to know before paying

A good screening test finds disease earlier than it would otherwise be found and leads to treatment that improves outcomes. It must also avoid causing more harm than good. Tests that detect many slow-growing or harmless abnormalities can cause overdiagnosis, with unnecessary biopsies and treatments. Because healthy people who are screened far outnumber those who benefit, even small harm rates can add up.

Whole-body imaging produces many images, and most findings in healthy people are incidental and harmless, such as cysts, nodules or minor variations. Following up these findings can lead to repeat scans, biopsies and anxiety. CT also involves radiation. There is no evidence that whole-body scanning in people without symptoms reduces deaths. Royal colleges and screening bodies do not recommend it for general screening, though imaging has a clear role when symptoms or specific risks exist.

Tests that look for fragments of tumour DNA in the blood aim to detect many cancers at once. They are an active area of research. Large trials are examining whether using them reduces late-stage cancer and deaths. Concerns include false positives, missed cancers, the possibility of detecting cancers that would not cause harm and the cost of follow-up. A normal result does not rule out cancer, and symptoms should still be investigated.

Blood tests for proteins associated with cancer, such as CA-125, CA 19-9 and CEA, can be raised in benign conditions and normal in cancers, which limits their usefulness for screening. They are mainly used to monitor people already diagnosed or, with imaging, to assess certain symptoms. Using them as general screening often leads to unnecessary worry and tests.

PSA is a blood marker that can rise with prostate cancer but also with benign enlargement, infection and recent ejaculation. Testing can find cancers early but also finds some that would never have caused problems. Treatment can cause erectile dysfunction and urinary problems. The NHS prostate cancer risk management programme allows men over 50 to request a PSA test after counselling. Men at higher risk, including Black men and those with a family history, may discuss earlier testing with their GP.

Consumer genetic tests can reveal variants of uncertain significance and are not diagnostic. Where there is a strong family history, referral to NHS genetics services is more appropriate. Other panels, such as broad hormone, inflammation or food intolerance tests, often have limited evidence of clinical benefit in healthy people.

Ask what question the test answers, what happens if it is abnormal and what happens if it is normal. Ask about harms as well as benefits. If you are at higher risk because of family history, discuss targeted options with your GP. If you have symptoms, do not rely on a screening test; seek assessment.