I read the recent letters regarding the bowel cancer screening “poo in the post” test (18 May) with an enduring sense of frustration regarding the lack of public awareness of what this test is actually meant to achieve and its implications for them.
Bowel cancer commonly gives rise to no symptoms, hence the need for a national screening programme. However, due to limited resources (colonoscopy capacity), this is set up to detect a group of asymptomatic people who would otherwise have gone undiagnosed, with the aim of benefiting us at a population level overall while acknowledging that some people with a negative test may have been falsely reassured that they do not have bowel cancer.
The new “poo test” called qFIT is highly sensitive, but the “q” stands for quantitative. That means that the threshold value of a positive test can be altered depending on the circumstances.
We have seen a lot in the media about pre-test probabilities and the meaning of a result in relation to Covid and lateral flow tests. For bowel cancer screening in England, given the assumption that the screening population has no symptoms, the threshold of a positive test is set at 120. But if you present to your GP with potential symptoms, you will be offered a test where it is considered positive if greater than 10 and then referred on for further investigations. For those with a result less than 10, your chance of having bowel cancer at an individual level is then less than 1%.
Damian Glancy
Consultant colorectal surgeon
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