{"entity":{"id":"faecal-occult-blood-test","kind":"term","name":"Faecal occult blood test (guaiac)","aka":["FOBT","gFOBT","guaiac faecal occult blood test","Haemoccult","hidden blood test","faecal occult blood screening"],"tldr":"The guaiac faecal occult blood test was the first stool test used for bowel screening: six smears from three separate stools, read by a colour change when blood is present. It is the test that proved in randomised trials that bowel screening saves lives, and England replaced it with the more accurate and easier faecal immunochemical test in 2019.","summary":"How it worked. The guaiac test detects the peroxidase activity of haem, so it reacts to any blood, including blood from meat in the diet, which is why dietary restrictions and repeat testing were part of the protocol. Participants smeared two samples from each of three consecutive stools onto six guaiac-impregnated paper slides.\n\nWhat it proved. Three randomised trials made the case for population bowel screening. In Minnesota, 46,551 people aged 50 to 80 were randomised to annual screening, biennial screening or no screening; annual testing with rehydrated samples cut 13-year colorectal cancer mortality by 33 percent, and biennial testing did not reach significance (Mandel 1993). In Nottingham, 152,850 people aged 45 to 74 were randomised to biennial testing or nothing, and colorectal cancer mortality fell 15 percent (odds ratio 0.85); 20 percent of the cancers in the screening arm were Dukes A against 11 percent in the control arm (Hardcastle 1996). These results are the reason national programmes exist.\n\nWhy it was replaced. The faecal immunochemical test uses an antibody to human haemoglobin, so it needs no dietary restriction, takes one sample rather than six, and gives a number rather than a colour change, which lets a programme choose its threshold. England switched every screening invitation to it in June 2019 (GOV.UK). The older test survives in the literature as the comparator in almost every screening trial, so its numbers are still the floor against which newer tests are judged.","asOf":"2026-09-24","wikipedia":"https://en.wikipedia.org/wiki/Fecal_occult_blood","links":[{"label":"Mandel, N Engl J Med 1993: reducing mortality from colorectal cancer by screening for faecal occult blood (Minnesota, 46,551 people)","url":"https://doi.org/10.1056/nejm199305133281901"},{"label":"Hardcastle, Lancet 1996: randomised controlled trial of faecal occult blood screening for colorectal cancer (Nottingham, 152,850 people)","url":"https://doi.org/10.1016/s0140-6736(96)03386-7"},{"label":"GOV.UK: NHS bowel cancer screening programme overview (target population and the screening test)","url":"https://www.gov.uk/guidance/bowel-cancer-screening-programme-overview"},{"label":"Atkin, Lancet 2017: UK Flexible Sigmoidoscopy Screening Trial, 17 years of follow-up (170,034 people)","url":"https://doi.org/10.1016/s0140-6736(17)30396-3"}],"tags":["gi","colorectal"],"related":[],"cancers":["colorectal","colon-cancer","rectal-cancer"],"sections":[],"technologies":["colorectal-screening"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["fit-test","bowel-cancer-screening-uk","screening-uptake","interval-cancer"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"Diagnostics & imaging"},"route":"/terms/faecal-occult-blood-test/","neighbours":{"cancer":[{"id":"colon-cancer","kind":"cancer","name":"Colon cancer (adenocarcinoma of the colon)","route":"/cancers/colon-cancer/"},{"id":"colorectal","kind":"cancer","name":"Colorectal cancer","route":"/cancers/colorectal/"},{"id":"rectal-cancer","kind":"cancer","name":"Rectal cancer","route":"/cancers/rectal-cancer/"}],"technology":[{"id":"colorectal-screening","kind":"technology","name":"Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood)","route":"/technologies/colorectal-screening/"}],"term":[{"id":"fit-test","kind":"term","name":"Faecal immunochemical test (FIT)","route":"/terms/fit-test/"},{"id":"interval-cancer","kind":"term","name":"Interval cancer","route":"/terms/interval-cancer/"},{"id":"bowel-cancer-screening-uk","kind":"term","name":"NHS bowel cancer screening programme","route":"/terms/bowel-cancer-screening-uk/"},{"id":"screening-uptake","kind":"term","name":"Screening uptake","route":"/terms/screening-uptake/"}]}}