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Worldwide, colorectal cancer (CRC) is the third most common form of cancer, after lung and breast cancer, and the fourth most common cause of cancer death, although in developed countries CRC incidence is higher and it accounts for an even higher proportion of cancer deaths.1
Screening for colorectal cancer reduces its mortality rate. Many countries have implemented population-based CRC screening programmes and many more are poised to do so. Whilst several different CRC screening modalities are available, choice will be influenced by cost, available resources (e.g. high-quality colonoscopy) and acceptability of the test by the invited population.2
The qualitative guaiac FOB test (gFOBT) detects the presence of faecal occult blood (FOB) and was historically used in many CRC screening programmes, however, this test has essentially been replaced in the UK by Faecal Immunochemical testing (FIT) for Haemoglobin (Hb). This is a much more specific test for bleeding from the colon or lower gastrointestinal tract, as it does not detect occult blood from the stomach and upper small intestine. The Weqas Qualitative Faecal Hb programme caters for laboratories using the qualitative FIT methods and those using the gFOBT kits.
1. Tests and investigations for colorectal cancer screening. Clin Biochem. 2014 Jul;47(10-11):921-39. doi: 10.1016/j.clinbiochem.2014.04.019. Epub 2014 Apr 24. Carroll MR1, Seaman HE2, Halloran SP3.
2. Faecal occult blood testing for colorectal cancer screening: the past or the future. Curr Gastroenterol Rep. 2015 Feb;17(2):428. doi: 10.1007/s11894-015-0428-2. Benton SC1, Seaman HE, Halloran SP.
Three samples are distributed on a monthly basis. Samples are prepared from organic material designed to simulate the composition of human faeces. The range of Hb in the material covers the pathological and analytical range for gFOBT and qualitative (FIT). Participants are assessed on their ability to correctly detect negative and positive samples with scores reflecting the concentration of Hb in the material and the clinical impact of an incorrect result. A correct result (in agreement with interpretive comment) is given a score of 0. A score of 4 is assigned for a gross misclassification of the result. A negative result for a positive sample is given a score between 1 and 4 depending on the Hb concentration of the sample, where 1 would relate to a sample with a Hb concentration at or close to the method “cut off” and 4 for a sample at a high Hb concentration. Any positive result for a negative sample is given a score of 3. The sensitivities of the methods and the intended purpose of the kits are also considered in the scores.
|Qualitative Faecal Hb (FHb) Programme|
|Analyte||Approx. Range Covered|
|FOB||0 - 3.5||mg Hb/g matrix|
|hsFOB||0 - 3.5||mg Hb/g matrix|
|Qualitative FIT||0 - 3500||µg Hb/g matrix|