Fecal occult blood
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|Fecal occult blood|
|Cards and bottle used for the Hemoccult test, a type of stool guaiac test|
|Classification and external resources|
Fecal occult blood (FOB) refers to blood in the feces that is not visibly apparent (unlike other types of blood in stool such as melena or hematochezia). A fecal occult blood test (FOBT) checks for hidden (occult) blood in the stool (feces).
- 1 Medical uses
- 2 Marathon runners
- 3 Nomenclature
- 4 Methodology
- 5 Test performance
- 6 References
- 7 External links
Fecal occult blood testing (FOBT), as its name implies, aims to detect subtle blood loss in the gastrointestinal tract, anywhere from the mouth to the colon. Positive tests ("positive stool") may result from either upper gastrointestinal bleeding or lower gastrointestinal bleeding and warrant further investigation for peptic ulcers or a malignancy (such as colorectal cancer or gastric cancer). The test does not directly detect colon cancer but is often used in clinical screening for that disease, but it can also be used to look for active occult blood loss in anemia or when there are gastrointestinal symptoms.
The stool guaiac test for hidden (occult) blood in the stool can be done at home or in the doctor's office, or can be performed on samples submitted to a clinical laboratory. Testing kits are available at pharmacies in some countries without a prescription, or a health professional may order a testing kit for use at home. If a home fecal occult blood test detects blood in the stool it is recommended to see a health professional to arrange further testing.
Source of bleeding
Gastrointestinal bleeding has many potential sources, and positive results usually result in further testing for the bleeding site, usually looking for lower gastrointestinal bleeding before upper gastrointestinal bleeding causes unless there are other clinical clues. Colonoscopy is usually preferred to computerized tomographic colonography.
- 2–10%: cancer (colorectal cancer, gastric cancer)
- 20–30% adenoma or polyps
- Diverticular disease
- Inflammatory bowel disease
- Angiodysplasia of the colon
- Sickle cell anemia
In the event of a positive fecal occult blood test, the next step in the workup is a form of visualization of the gastrointestinal tract by one of several means:
- Sigmoidoscopy, an examination of the rectum and lower colon with a lighted instrument to look for abnormalities, such as polyps.
- Colonoscopy, a more thorough examination of the rectum and entire colon.
- Virtual colonoscopy
- Upper gastrointestinal endoscopy. It is sometimes performed with chromoendoscopy, a method that assists the endoscopist by enhancing the visual difference between cancerous and normal tissue, either by marking the abnormally increased DNA content (toluidine blue) or failing to stain the tumor, possibly due to decreased surface glycogen on tumor cells(Lugol). Infrared fluorescent endoscopy and ultrasonic endoscopy can interrogate vascular abnormalities such as esophageal varices.
- Double contrast barium enema: a series of x-rays of the colon and rectum.
Although red or black stools can be an indication of bleeding, a dark or black color can be due to black licorice, blueberries, iron supplements, lead, Pepto-bismol, and a red color can come from natural or artificial coloring such as red gelatin, popsicles, Kool-Aid, and large amounts of beets.
Colorectal cancer screening
Screening methods for colon cancer depend on detecting either precancerous changes such as certain kinds of polyps or on finding early and thus more treatable cancer. The extent to which screening procedures reduce the incidence of gastrointestinal cancer or mortality depends on the rate of precancerous and cancerous disease in that population. gFOBT and flexible sigmoidoscopy screening have each shown benefit in randomized clinical trials. Evidence for other colon cancer screening tools such as iFOBT or colonoscopy is substantial and guidelines have been issued by several advisory groups but does not include randomized studies.
In 2009 the American College of Gastroenterology (ACG) suggest that colon cancer screening modalities that are also directly preventive by removing precursor lesions should be given precedence, and prefer a colonoscopy every 10 years in average-risk individuals, beginning at age 50. The ACG suggests that cancer detection tests such as any type of FOB are an alternative that is less preferred and if an colonoscopy is declined the FIT should be offered instead. Two other recent guidelines, from the US Multisociety Task Force (MSTF) and the US Preventive Services Task Force (USPSTF) while permitting immediate colonoscopy as an option, did not categorize it as preferred. The ACG and MSTF also included CT colonography every five years, and fecal DNA testing as considerations. All three recommendation panels recommended replacing any older low-sensitivity, guaiac-based fecal occult blood testing (gFOBT) with either newer high-sensitivity guaiac-based fecal occult blood testing (hs gFOBT) or fecal immunochemical testing (FIT). MSTF looked at six studies that compared high sensitivity gFOBT (Hemoccult SENSA) to FIT, and concluded that there was no clear difference in overall performance between these methods.
The American College of Gastroenterology has recommended the abandoning of gFOBT testing as a colorectal cancer screening tool, in favor of the fecal immunochemical test. Though the FIT test is preferred, even the guaiac FOB testing of average risk populations may have been sufficient to reduce the mortality associated with colon cancer by about 25%. With this lower efficacy, it was not always cost effective to screen a large population with gFOBT.
If colon cancer is suspected in an individual (such as in someone with an unexplained anemia) fecal occult blood tests may not be clinically helpful. If a doctor suspects colon cancer, more rigorous investigation is necessary, whether or not the test is positive.
In 2006, the Australian Government introduced the National Bowel Cancer Program which has been updated several times since; targeted screening will be done of all Australians aged over 50 to 74 by 2017–2018. Cancer Council Australia recommended that FOBT should be done every two years. Gradually government fund disbursement meant that some people are not yet eligible for the national program and should pay for a FOBT by themselves.
The use of the M2-PK Test is encouraged over gFOBT for routine screening as it may pick up tumors that are both bleeding and non bleeding. It is able to pick up 80 percent of colorectal cancer and 44 percent for adenoma > 1 centimeter, while gFOBT picks up 13 to 50 percent of colorectal cancers.
Iron deficiency anemia
An extensive literature has examined the clinical value of FOBT in iron deficiency anemia.
Gastrointestinal disease and medications
Conditions such as ulcerative colitis or certain types of relapsing infectious diarrhea can vary in severity over time, and FOBT may assist in assessing the severity of the disease. Medications associated with gastrointestinal bleeding such as Bortezomib are sometimes monitored by FOBT.
Testing secretions for occult blood
The use of tests for occult blood in disorders of the mouth, nasal passages, esophagus, lungs and stomach, while analogous to fecal testing, is often discouraged, due to technical considerations including poorly characterized test performance characteristics such as sensitivity, specificity, and analytical interference. However, chemical confirmation that coloration is due to blood rather than coffee, beets, medications, or food additives can be of significant clinical assistance.
A related concept to colon cancer screening by FOBT, based on most neoplasms affecting the surface epithelium and losing small amounts of blood but no visible blood loss, is screening in populations at high risk for esophageal or gastric cancers by testing for blood by swallowing a small capsule that is recovered after 3 to 5 minutes by gentle retrieval by means of an attached nylon thread.
Gastrointestinal (GI) complaints and low intensity GI bleeding frequently occur in marathon runners. Strenuous exercise, particularly in elite athlete runners and less frequently in other exercise activities, can cause acute incapacitating gastrointestinal symptoms including heartburn, nausea, vomiting, abdominal pain, diarrhea and gastrointestinal bleeding. Approximately one third of endurance runners experience transient but exercise limiting symptoms, and repetitive gastrointestinal bleeding occasionally causes iron deficiency and anaemia. Runners can sometimes experience significant symptoms including hematemesis. Exercise is associated with extensive changes in gastrointestinal (GI) tract physiology, including diversion of blood flow from the GI tract to muscle and lungs, decreased GI absorption and small intestinal motility, increased colonic transit, neuroimmunoendocrine changes in hormones and peptides such as vasoactive intestinal peptide, secretin and peptide-histidine-methionine. Substantial changes occur in stress hormones including cortisol, in circulating concentrations and metabolic behavior of various leucocytes, and in immunoglobulin levels and major histocompatibility complex expression. Symptoms can be exacerbated by dehydration or by pre-exercise ingestion of certain foods and hypertonic liquids, and lessened by adequate training.
Ingestion of 800 mg of cimetidine 2 hr before running a marathon did not significantly affect the frequency of gastrointestinal symptoms or occult gastrointestinal bleeding. Conversely, 800 mg of cimetidine 1 hr before the start and again at 50 miles of a 100-mile running race substantially decreased GI symptoms and postrace guaiac test positivity but did not affect race performance.
In 2007 the nomenclature of overt, obscure and occult bleeding was clarified.
There are four methods in clinical use for testing for occult blood in feces. These look at different properties, such as antibodies, heme, globin, or porphyrins in blood, or at DNA from cellular material such as from lesions of the intestinal mucosa.
- Fecal immunochemical testing (FIT), and immunochemical fecal occult blood test (iFOBT). FIT products utilize specific antibodies to detect globin. FIT screening is more effective in terms of health outcomes and cost compared with guaiac FOBT. According to the guidelines of the American College of Gastroenterology, "Annual fecal immunochemical testing is the preferred colorectal cancer detection test." A FIT test detects globin levels in feces at or above 50 nanograms per mL, the established cutoff by the World Health Organization for Colorectal Cancer Screening.
FIT testing has replaced most gFOBT tests as the colon cancer screening test of choice. This methodology can be adapted for automated test reading and to report quantitative results, which are potential factors in design of a widescale screening strategy. The number of fecal samples submitted for FIT may affect the clinical sensitivity and specificity of the methodology. High sensitivity gFOBT tests such as Hemoccult SENSA remains an accepted option; and may retain a role in monitoring gastrointestinal conditions such as ulcerative colitis; however the FIT test is preferred in recent guidelines.
- Stool guaiac test for fecal occult blood (gFOBT): – The stool guaiac test involves smearing some feces onto some absorbent paper that has been treated with a chemical. Hydrogen peroxide is then dropped onto the paper; if trace amounts of blood are present, the paper will change color in one or two seconds. This method works as the heme component in hemoglobin has a peroxidase-like effect, rapidly breaking down hydrogen peroxide. In some settings such as gastric or proximal upper intestinal bleeding the guaiac method may be more sensitive than tests detecting globin because globin is broken down in the upper intestine to a greater extent than is heme. There are various commercially available gFOBT tests which have been categorized as being of low or high sensitivity, and only high sensitivity tests remain an acceptable alternative to FIT testing, which is now the best-practices recommendation in colon cancer screening. Optimal clinical performance of the stool guaiac test depends on preparatory dietary adjustment.
- Stool DNA screening test look for DNA alterations that have been associated with cancer.
The estimates for test performance characteristics are based on comparison with a variety of reference methods including 51-chromium studies, analytical recovery studies in spiked stool samples, analytical recovery after ingestion of autologous blood, rarer studies of carefully quantified blood instilled at bowel surgery as well as other research approaches. Additionally, clinical studies look at variety of additional factors.
Gastrointestinal blood loss
In healthy people about 0.5 to 1.5 ml of blood escapes blood vessels into the stool each day. Significant amounts of blood can be lost without producing visible blood in the stool, estimated as 200 ml in the stomach, 100 ml in the duodenum, and lesser amounts in the lower intestine. Tests for occult blood identify lesser blood loss.
Clinical sensitivity and specificity
Fecal Immunochemical Testing (FIT) picks up as little as 0.3 ml of blood in the stool; yet this test threshold doesn't cause undue false positives from normal upper intestinal blood leakage because it does not detect occult blood from the stomach and upper small intestine. Thus the FIT test is much more specific for bleeding from the colon or lower gastrointestinal tract than alternatives. The detection rate of the test decreases if the time from sample collection to laboratory processing is delayed; processing the sample in under five days from collection is recommended.
Stool guaiac test for fecal occult blood (gFOBT) sensitivity varies depending on the site of bleeding. Moderately sensitive gFOBT can pick up a daily blood loss of about 10 ml (about two teaspoonfuls), and higher sensitivity gFOBT can pick up lesser amounts, requires at least 2 ml. to become positive. The sensitivity of a single stool guaiac test to pick up bleeding has been quoted at 10 to 30%, but if a standard three tests are done as recommended the sensitivity rises to 92%. Reduced patient compliance with the collection of three samples hampers the usefulness of this test. Further discussion of sensitivity and specificity issues that relate particularly to the guaiac method is found in the stool guaiac test article.
Fecal porphyrin quantification by HemoQuant can be false positive due to exogenous blood and various porphyrins. HemoQuant is the most sensitive test for upper gastrointestinal bleeding and therefore may be most appropriate fecal occult blood test to use in the evaluation of iron deficiency Advised to stop red meat and aspirin for three days prior to specimen collection False positives can occur with myoglobin, catalase, or protohemes and in certain types of porphyria.
Fecal DNA tests as of 2008 had not been well studied enough to support widespread use.
- Beg M; et al. (2002). "Occult Gastrointestinal Bleeding: Detection, Interpretation, and Evaluation" (PDF). JIACM. 3 (2): 153–58. Archived from the original (PDF) on 2010-11-22.
- Harewood GC, Ahlquist DA (2000). "Fecal occult blood testing for iron deficiency: a reappraisal". Dig Dis. 18 (2): 75–82. doi:10.1159/000016968. PMID 11060470.
- Bardhan PK, Beltinger J, Beltinger RW, Hossain A, Mahalanabis D, Gyr K (January 2000). "Screening of patients with acute infectious diarrhoea: evaluation of clinical features, faecal microscopy, and faecal occult blood testing". Scand. J. Gastroenterol. 35 (1): 54–60. doi:10.1080/003655200750024533. PMID 10672835.
- "Fecal Occult Blood Test (FOBT)". Retrieved 2007-07-18.
- Rockey DC (December 2005). "Occult gastrointestinal bleeding". Gastroenterol. Clin. North Am. 34 (4): 699–718. doi:10.1016/j.gtc.2005.08.010. PMID 16303578.
- Walleser S, Griffiths A, Lord SJ, Howard K, Solomon MJ, Gebski V (December 2007). "What is the value of computerized tomographic colonography in patients screening positive for fecal occult blood? A systematic review and economic evaluation". Clin. Gastroenterol. Hepatol. 5 (12): 1439–46; quiz 1368. doi:10.1016/j.cgh.2007.09.003. PMID 18054752.
- Bevan R; Lee TJ; Nickerson C; Rubin G; Rees CJ; NHS BCSP Evaluation Group (June 2014). "Non-neoplastic findings at colonoscopy after positive faecal occult blood testing: data from the English Bowel Cancer Screening Programme". J. Med. Screen. 21 (2): 89–94. doi:10.1177/0969141314528889. PMID 24644029.
- Endo M, Sakakibara N, Suzuki H. Observation of esophageal lesions with the use of endoscopic dyes. Progress of Digestive Endoscopy. 1972; 1: 34.
- Endo M, Takeshita K, Yoshida M (September 1986). "How can we diagnose the early stage of esophageal cancer? Endoscopic diagnosis". Endoscopy. 18 Suppl 3: 11–8. doi:10.1055/s-2007-1018435. PMID 2428607.
- Rex DK, Johnson DA, Anderson JC, Schoenfeld PS, Burke CA, Inadomi JM (March 2009). "American College of Gastroenterology guidelines for colorectal cancer screening 2009 [corrected]". Am. J. Gastroenterol. 104 (3): 739–50. doi:10.1038/ajg.2009.104. PMID 19240699.
- Levin, B.; Lieberman, D. A.; McFarland, B.; Smith, R. A.; Brooks, D.; Andrews, K. S.; Dash, C.; Giardiello, F. M.; Glick, S.; Levin, T. R.; Pickhardt, P.; Rex, D. K.; Thorson, A.; Winawer, S. J. (2008). "Screening and Surveillance for the Early Detection of Colorectal Cancer and Adenomatous Polyps, 2008: A Joint Guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology". CA: A Cancer Journal for Clinicians. 58 (3): 130–60. doi:10.3322/CA.2007.0018. PMID 18322143.
- USPSTF Agency for Healthcare Research and Quality. Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2008; 149: 627–37. Also available at Screening for colorectal cancer, topic page: http://www.uspreventiveservicestaskforce.org/uspstf/uspscolo.htm accessioned 2010 October 26, which has several hyperlink extensions to several extensive reviews, including accessible articles with recommendation statements, clinical background summary, decision analysis, systematic review, and evidence synthesis.
- Rex, DK; Johnson, DA; Anderson, JC; Schoenfeld, PS; Burke, CA; Inadomi, JM; American College of, Gastroenterology (Mar 2009). "American College of Gastroenterology guidelines for colorectal cancer screening 2009 [corrected].". The American journal of gastroenterology. 104 (3): 739–50. doi:10.1038/ajg.2009.104. PMID 19240699.
- Bretthauer M (August 2010). "Evidence for colorectal cancer screening". Best Pract Res Clin Anaesthesiol. 24 (4): 417–25. doi:10.1016/j.bpg.2010.06.005. PMID 20833346.
- Mandel JS, Bond JH, Church TR, et al. (May 1993). "Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study". N. Engl. J. Med. 328 (19): 1365–71. doi:10.1056/NEJM199305133281901. PMID 8474513.
- Hardcastle JD, Chamberlain JO, Robinson MH, et al. (November 1996). "Randomised controlled trial of faecal-occult-blood screening for colorectal cancer". Lancet. 348 (9040): 1472–7. doi:10.1016/S0140-6736(96)03386-7. PMID 8942775.
- Kronborg O, Fenger C, Olsen J, Jørgensen OD, Søndergaard O (November 1996). "Randomised study of screening for colorectal cancer with faecal-occult-blood test". Lancet. 348 (9040): 1467–71. doi:10.1016/S0140-6736(96)03430-7. PMID 8942774.
- Kewenter J, Brevinge H, Engarås B, Haglind E, Ahrén C (May 1994). "Results of screening, rescreening, and follow-up in a prospective randomized study for detection of colorectal cancer by fecal occult blood testing. Results for 68,308 subjects". Scand. J. Gastroenterol. 29 (5): 468–73. doi:10.3109/00365529409096840. PMID 8036464.
- "Bowel cancer screening". Retrieved July 4, 2013.
- "Screening for colorectal cancer". Canadian Cancer Society. Canadian Cancer Society. Retrieved July 14. Check date values in:
- Collins JF, Lieberman DA, Durbin TE, Weiss DG (January 2005). "Accuracy of screening for fecal occult blood on a single stool sample obtained by digital rectal examination: a comparison with recommended sampling practice". Ann. Intern. Med. 142 (2): 81–85. doi:10.7326/0003-4819-142-2-200501180-00006. PMID 15657155.
- Tonus, C; Sellinger, M; Koss, K; Neupert, G (14 August 2012). "Faecal pyruvate kinase isoenzyme type M2 for colorectal cancer screening: a meta-analysis.". World journal of gastroenterology : WJG. 18 (30): 4004–11. doi:10.3748/wjg.v18.i30.4004. PMC . PMID 22912551.
- Qin DX; Wang GQ; Zuo JH; et al. (January 1993). "Screening of esophageal and gastric cancer by occult blood bead detector". Cancer. 71 (1): 216–18. doi:10.1002/1097-0142(19930101)71:1<216::AID-CNCR2820710133>3.0.CO;2-#. PMID 8416718.
- Adams BD, McHugh KJ, Bryson SA, Dabulewicz J (February 2008). "The law of unintended consequences: The Joint Commission regulations and the digital rectal examination". Ann Emerg Med. 51 (2): 197–201, 201.e1. doi:10.1016/j.annemergmed.2007.07.022. PMID 17961818.
- Cleveland NJ, Yaron M, Ginde AA (August 2010). "The effect of removal of point-of-care fecal occult blood testing on performance of digital rectal examinations in the emergency department". Ann Emerg Med. 56 (2): 135–41. doi:10.1016/j.annemergmed.2009.12.021. PMID 20060198.
- Halvorsen FA, Lyng J, Ritland S (May 1986). "Gastrointestinal bleeding in marathon runners". Scand. J. Gastroenterol. 21 (4): 493–97. doi:10.3109/00365528609015168. PMID 3487825.
- de Oliveira EP, Burini RC (September 2009). "The impact of physical exercise on the gastrointestinal tract". Curr Opin Clin Nutr Metab Care. 12 (5): 533–38. doi:10.1097/MCO.0b013e32832e6776. PMID 19535976.
- Peters HP, De Vries WR, Vanberge-Henegouwen GP, Akkermans LM (March 2001). "Potential benefits and hazards of physical activity and exercise on the gastrointestinal tract". Gut. 48 (3): 435–39. doi:10.1136/gut.48.3.435. PMC . PMID 11171839.
- Weaver LT (1984). "Do some marathon runners bleed into the gut? (letter response to a previous article)" (PDF). BMJ. 288 (6410): 65. doi:10.1136/bmj.288.6410.65-b. PMC .
- Brouns F, Beckers E (April 1993). "Is the gut an athletic organ? Digestion, absorption and exercise". Sports Med. 15 (4): 242–57. doi:10.2165/00007256-199315040-00003. PMID 8460288.
- Venkatraman JT, Pendergast DR (2002). "Effect of dietary intake on immune function in athletes". Sports Med. 32 (5): 323–37. doi:10.2165/00007256-200232050-00004. PMID 11929359.
- Moses FM, Baska RS, Peura DA, Deuster PA (October 1991). "Effect of cimetidine on marathon-associated gastrointestinal symptoms and bleeding". Dig. Dis. Sci. 36 (10): 1390–4. doi:10.1007/BF01296804. PMID 1914760.
- Baska RS, Moses FM, Deuster PA (August 1990). "Cimetidine reduces running-associated gastrointestinal bleeding. A prospective observation". Dig. Dis. Sci. 35 (8): 956–60. doi:10.1007/BF01537243. PMID 2384041.
- Quintero, E. (2009). "¿Test químico o test inmunológico para la detección de sangre oculta en heces en el cribado del cáncer colorrectal?". Gastroenterología y Hepatología. 32 (8): 565–576. doi:10.1016/j.gastrohep.2009.01.179. PMID 19577340.
- Rex, Douglas K.; Johnson, David A.; Anderson, Joseph C.; Schoenfeld, Phillip S.; Burke, Carol A.; Inadom, John M. (24 Feb 2009). "American College of Gastroenterology Guidelines for Colorectal Cancer Screening 2008" (PDF). Am J Gastroenterol (advance online publication). 104: 739–50. doi:10.1038/ajg.2009.104. PMID 19240699.
- Colorectal Cancer http://patients.gi.org/topics/colorectal-cancer
- Young GP, Cole SR (March 2009). "Which fecal occult blood test is best to screen for colorectal cancer?". Nat Clin Pract Gastroenterol Hepatol. 6 (3): 140–41. doi:10.1038/ncpgasthep1358. PMID 19174764.
- Quintero E (October 2009). "[Chemical or immunological tests for the detection of fecal occult blood in colorectal cancer screening?]". Gastroenterol Hepatol (in Spanish). 32 (8): 565–76. doi:10.1016/j.gastrohep.2009.01.179. PMID 19577340.
- Berchi C, Bouvier V, Réaud JM, Launoy G (March 2004). "Cost-effectiveness analysis of two strategies for mass screening for colorectal cancer in France". Health Econ. 13 (3): 227–38. doi:10.1002/hec.819. PMID 14981648.
- Kuriyama M, Kato J, Takemoto K, Hiraoka S, Okada H, Yamamoto K (March 2010). "Prediction of flare-ups of ulcerative colitis using quantitative immunochemical fecal occult blood test". World J. Gastroenterol. 16 (9): 1110–14. doi:10.3748/wjg.v16.i9.1110. PMC . PMID 20205282.
- Rockey DC (July 1999). "Occult gastrointestinal bleeding". N. Engl. J. Med. 341 (1): 38–46. doi:10.1056/NEJM199907013410107. PMID 10387941.
- "Diagnostic Tests — Fecal Occult Blood Test". Retrieved 2007-07-18.
- Sheng JQ; Li SR; Wu ZT; et al. (August 2009). "Transferrin dipstick as a potential novel test for colon cancer screening: a comparative study with immuno fecal occult blood test" (PDF). Cancer Epidemiol. Biomarkers Prev. 18 (8): 2182–85. doi:10.1158/1055-9965.EPI-09-0309. PMID 19661074.
- Sheng JQ; Li SR; Su H; et al. (June 2010). "Fecal cytology in conjunction with immunofecal occult blood test for colorectal cancer screening". Anal. Quant. Cytol. Histol. 32 (3): 131–5. PMID 20701065.
- Ahlquist DA, McGill DB, Schwartz S, Taylor WF, Owen RA (May 1985). "Fecal blood levels in health and disease. A study using HemoQuant". N. Engl. J. Med. 312 (22): 1422–8. doi:10.1056/NEJM198505303122204. PMID 3873009.
- Dybdahl JH, Daae LN, Larsen S (1981). "Occult faecal blood loss determined by chemical tests and a 51 Cr method". Scand. J. Gastroenterol. 16 (2): 245–52. doi:10.3109/00365528109181963. PMID 7313535.
- St John DJ, Young GP (April 1978). "Evaluation of radiochromium blood loss studies in unexplained iron-deficiency anaemia". Aust N Z J Med. 8 (2): 121–6. doi:10.1111/j.1445-5994.1978.tb04496.x. PMID 307949.
- Schiff L, Stevens RJ, Shapiro N, et al. Observations on the oral administration of citrate blood in man. Am J Med Sci 1942; 203: 409.
- "What Does a Positive Fecal Occult Blood Test Mean? – B01". Retrieved 2007-07-18.
- van Rossum LG; van Rijn AF; van Oijen MG; et al. (August 2009). "False negative fecal occult blood tests due to delayed sample return in colorectal cancer screening". Int. J. Cancer. 125 (4): 746–50. doi:10.1002/ijc.24458. PMID 19408302.
- "Screening average risk patients for colorectal cancer – B01". Retrieved 2007-10-25.
- Harewood GC, McConnell JP, Harrington JJ, Mahoney DW, Ahlquist DA (January 2002). "Detection of occult upper gastrointestinal tract bleeding: performance differences in fecal occult blood tests". Mayo Clin. Proc. 77 (1): 23–28. doi:10.4065/77.1.23. PMID 11794453.
- Title etc http://www.mayomedicallaboratories.com/test-catalog/Overview/9220 acc on etc
- Schwartz S, Dahl J, Ellefson M, Ahlquist D (December 1983). "The "HemoQuant" test: a specific and quantitative determination of heme (hemoglobin) in feces and other materials". Clin. Chem. 29 (12): 2061–67. PMID 6640900.
- Whitlock EP, Lin J, Liles E, Beil T, Fu R, O'Connor E, Thompson RN, Cardenas T (2008). "Screening for Colorectal Cancer: An Updated Systematic Review". Agency for Healthcare Research and Quality (US). PMID 20722162. Report No.: 08-05-05124-EF-1.
- FOBT Overview at Mayo Clinic
- Overview at Cleveland Clinic
- ColonCancerCheck including fact sheets in 24 languages at Ontario Ministry of Health and Long-Term Care
- Burt RW (September 2010). "Colorectal cancer screening". Curr Opin Gastroenterol. 26: 466–70. doi:10.1097/MOG.0b013e32833d1733. PMID 20664346.