Does Genetic Susceptibility for Bleeding Affect Quantitative Faecal Immunochemical Test (qFIT) Results?

Plain-language summary

Quantitative faecal immunochemical testing (qFIT) is used to test for blood within faeces that cannot always be visible. The presence of blood in the stool has been shown to be a finding where there may be a problem within the large bowel. The test is able to give a numeric value to the blood in the stool and based on this result, further investigations can be planned, or if normal reassurance given. The test is not perfect and minor bowel problems such as haemorrhoids (piles) can give a raised result. However, we have also seen raised results in people who when investigated have a completely normal large bowel. A small degree of 'physiological' non-visible bleeding is likely a normal part of life and for the majority this does not lead to a raised qFIT result. It may be the case in people who have a raised qFIT but then go on to have a completely normal colonoscopy (telescope investigation of the large bowel) that there is a genetic predisposition that increases the amount of normal 'physiological blood' that they produce. This leads to the test being falsely positive and the person undergoing an unnecessary investigation. This study aims to use saliva to test for known genetic markers that effect blood clotting and can increase how much someone bleeds. By comparing the occurrence of these genetic markers in people with a raised qFIT and normal colonoscopy to those with a normal qFIT and normal colonoscopy, we can test this theory. Should this be the case it will help explain why the test can be raised in normal large bowel and could lead to different levels of positivity being used for different people.

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