Faecal Haemoglobin in the Scottish Bowel Screening Programme

The introduction of the faecal immunochemical test (FIT) into the Scottish Bowel Screening Programme, and replacement of the guaiac faecal occult blood test (gFOBT) in Scotland as a result, allowed investigation of several topics pertinent to colorectal cancer (CRC) screening. This thesis documents that many of the expected benefits of FIT in comparison to gFOBT are found in practice, particularly increased uptake (especially for hard-toreach groups) and improved adenoma detection. Such national screening interventions are typically implemented following a pilot evaluation, and evidence is presented here that such evaluations can mislead if variables are not held constant, since uptake and positivity both varied significantly from pilot to subsequent national roll-out. The data in this thesis give further insight into some of the factors affecting faecal haemoglobin concentration (f-Hb), with novel data on how this changes from the first to the second round of FIT for different first-round outcomes. Furthermore, previously published evidence for associations between increasing f-Hb and increasing age, male sex, and increased socioeconomic deprivation are confirmed in a large population. f-Hb variation within the country is also documented, with evidence that this varies between NHS Boards, even when holding socioeconomic deprivation quintile constant. Finally, the sex inequity in CRC screening is explored. Firstly, women with a screening-detected cancer are shown to have lower f-Hb than men, implying that proportionately more CRC in women will fall below a single threshold for referral than with men. Secondly, the consequences of this are documented using interval cancer proportions (ICP). Evidence is presented that shows ICP to be higher in women than men, and that this would be true of any f-Hb threshold implemented. Strategies to eliminate this sex inequity are discussed, with a particular emphasis on differential thresholds for women and men.