The relationship between faecal haemoglobin concentration and risk of significant colorectal neoplasia in screening and symptomatic populations.
Faecal immunochemical tests for haemoglobin (FIT) are replacing traditional guaiac-based faecal occult blood (gFOBT) tests in bowel screening programmes due to their many advantages. An evaluation of using quantitative FIT within the Scottish Bowel Screening Programme (SBSP) has taken place with faecal haemoglobin (Hb) concentration recorded for 38,720 participants. Subsequently, it has been established that faecal Hb concentration is related to severity of colorectal neoplastic disease, with higher median faecal Hb concentration in participants with advanced neoplasia compared to those with less severe outcomes (200.0 v. 166.0 µg Hb/g faeces, p < 0.0001). Those with elevated faecal Hb concentration (60.0 - 79.9 µg Hb/g faeces) at the time of a negative test result (< 80.0 µg Hb/g faeces) were more likely to be later diagnosed with an interval cancer than those with undetectable Hb (adjusted odds ratio = 24.7, 95% CI: 4.9 - 124.6). Follow-up of participants with a negative test result then testing positive in the subsequent screening round allowed calculation of an adjusted odds ratio of 38.0 (95% CI: 20.2 – 71.2) for advanced neoplasia in those with initial faecal Hb concentration 60.0 - 79.9 µg Hb/g faeces compared to those with faecal Hb concentration < 20.0 µg Hb/g faeces. These results give firm support to the role of faecal Hb concentration as a strong predictor of future risk of advanced neoplasia. The use of FIT in symptomatic patients was also evaluated, with results showing that using a cut-off faecal Hb concentration of any detectable Hb would have ruled out colorectal cancer and could have reduced the referral rate by 40%. With introduction of FIT now approved for the SBSP, it is hoped that a risk scoring system can be developed based on age, gender and faecal Hb concentration to better direct colonoscopy resource and reduce the proportion of interval cancers.
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