All screening interventions have the potential to do harm and screening by faecal occult blood testing (FOBT) is no exception. The harm arises not from the test itself, although the psychological impact is not negligible, but mainly from the investigation and treatment of test positives. The benefits of FOBT have been studied extensively and it seems that among those who comply with biennial testing, colorectal cancer mortality is significantly reduced1-3 and that the reduction is greater when the test is used annually.4 But there is a price to pay. Firstly, there is the anxiety engendered by performing the test itself and the greater anxiety induced in those who are found to be positive requiring further investigation. Although this has been shown to be short-lived, lasting mainly until the completion of diagnostic investigations, cumulatively it might be expected to affect around 10% of those complying with the test biennially over 20 years.

Secondly, there are the well documented complications associated with colonoscopy, which is considered the gold standard for the diagnostic workup …