Safety risks for patients can be reduced by giving special attention to the management of patients with co-morbidities. Also the threshold of positivity of tests can influence the number of colonoscopies performed and thus safety.

Further education of GPs regarding the appropriateness of referrals for gFOBT in patients with major co-morbidities is important, because complications related to colonoscopy are increased in patients with major co-morbidites. {13}

• [NHS Centre for Reviews and Dissemination : Diagnostic Accuracy and Cost-Effectiveness of Faecal Occult Blood Tests Used in Screening for Colorectal Cancer: A Systematic Review, 2007] {8}

Changing the threshold for positivity (e.g. the number of windows required to show blue colouration on a Haemoccult slide) may change both the sensitivity and specificity of the test. Some studies stated that ‘any blue colour’ indicated a positive result, others specified that 2, 3 or more windows had to show a blue colouration to be positive, and some studies retested after what were considered ‘weak’ positive results. These differences in threshold will affect the observed positivity rate of the test, and as such, will impact on the proposed number of colonoscopies that would be required as a result of a screening programme with FOBT.