Test immunochimique fécal quantitatif pour l’exploration de patients symptomatiques: une révolution venue des îles britanniques

Quantitative faecal immunochemical tests (FITs) are no longer reserved for the organised colorectal cancer screening programme. Biogroup laboratories in some area have been replacing qualitative FITs with a quantitative FIT (FOB Gold) for around 1 year, with automated analysis using a multi-purpose routine machine. The sensitivity of qualitative FITs for detecting an advanced neoplasm (CRC or advanced adenoma, i.e. adenoma ≥ 10 mm or high-grade dysplasia or villous or tubulocaval) varies considerably (30% to 73%). In the symptomatic population, sensitivity for CRC is also highly variable, ranging from 82% to 100%, with positivity rates varying from 22% to 35%. These poor results point to the obsolescence of qualitative FITs. In asymptomatic people at average risk of CRC, the sensitivity of the quantitative FIT for diagnosing CRC is 76% at the 10 µg/g threshold and 65% at the 20 µg/g threshold. Lowering the threshold to 20 µg/g would offer better sensitivity, estimated at between 87% and 91% (21% and 25% for advanced adenoma) for a positivity rate of 5.3%, which is perfectly manageable for French gastroenterologists. In symptomatic patients, the performances of the quantitative FITs have sensitivities for the diagnosis of CRC of 91.0% and 94.7% for thresholds set at 10 µg/g and at the limit of detection (2 µg/g). To date, three countries have published recommendations on the use of quantitative FITs for the investigation of symptomatic patients in general practice: the United Kingdom, Spain and Australia, all at a threshold of ≥ 10 µg/g. At the threshold of 2 µg/g, the sensitivity of the quantitative FIT for CRC is evaluated at 94.7% (between 93% and 100% depending on the study), equivalent to that of colonoscopy, and enables colonoscopy to be avoided in 66% of cases. It has been shown that only a minority of people with a family history of CRC are properly screened. It is paradoxical and counter-productive that 50-74-year-olds at high or supposedly high risk of CRC should be subject to the vagaries of opportunistic screening and excluded from the organised screening programme. This is a French exception: most organised screening programmes invite the entire population in the age group concerned to undergo screening, unless they expressly object.