Tools
Fecal Occult Blood Test
Introduction
The fecal occult blood test (FOBT) is a diagnostic test to assess for hidden (occult) blood in the stool. This test is commonly used for colorectal cancer screening, especially in developed nations. Colon cancer is one of the most prevalent cancers in both men and women worldwide. Therefore, early detection is imperative. When used correctly for screening, this testing modality has established associations with decreased morbidity and mortality.[1] Newer screening methods have been developed, including the fecal immunochemical test (FIT). FIT uses antibodies to discern blood in the stool. These newer modalities have replaced the FOBT for colon cancer screening due to increased specificity, sensitivity, and decreased costs.[2]
When blood enters the upper gastrointestinal tract, the globin part of the hemoglobin molecule is completely digested by the proteolytic enzymes; the heme is converted by bacterial action to porphyrins. Hemoglobin entering the lower part of the large intestine is largely undigested. In normal subjects, the volume of blood lost from the gastrointestinal tract is 0.5 to 1.5 mL per day. The fecal occult blood test does not usually detect this amount of blood.[3]
Standard methods for detecting occult blood are based on detecting hemoglobin or its breakdown products.[4] Fecal blood can also be detected by macroscopic examination of feces for blood cells or hematin crystals or by spectroscopic identification of hemoglobin and its derivatives.[5]
Specimen Collection
Register For Free And Read The Full Article
Search engine and full access to all medical articles- 10 free questions in your specialty
- Free CME/CE Activities
- Free daily question in your email
- Save favorite articles to your dashboard
- Emails offering discounts
Learn more about a Subscription to StatPearls Point-of-Care
Specimen Collection
The fecal occult blood test (FOBT) can be performed in the inpatient or outpatient setting. In the inpatient setting, the stool may be obtained manually during a digital rectal examination and placed onto heme occult testing cards. In the outpatient setting, the patient typically obtains a stool sample at home and then submits it to a laboratory.[6]
Feces should ideally be sampled before they come into contact with the toilet water since hemoglobin will leach out of the sample, and toilet sanitizers may affect the results. Because blood may not be uniformly distributed within the stools, and bleeding may be intermittent, it is important to collect samples from more than one area; collection should be repeated on three different days.[7]
It is best not to expose the sample to extreme heat or humidity; dried samples can be stored at room temperature for 14 days.[8] If there is a delay between sample collection and analysis, false-negative results may be seen because of the degradation of the pseudoperoxidase activity of heme in moist feces. If samples are collected directly onto the filter paper in the test kit and allowed to dry, this problem can be prevented.[9]
In some immunological methods, collection devices with liquid preservatives are used, and samples from patients can be collected by smearing the stools onto the card provided.[10] For most methods, some patient preparation is required to give optimum results. Samples should not be collected if blood is visible in the stools or urine (e.g., menstruation, active hemorrhoids, or urinary tract infection).[5]
Procedures
Before stool collection and testing, it is imperative to ensure that the FOBT card and developer are not beyond their expiration dates. Tests commonly used in clinical laboratories are based on detecting hemoglobin, heme, or heme-derived porphyrins.[11] Hemoglobin is detected by immunological methods, heme by guaiac-based methods utilizing the pseudoperoxidase activity of heme, and porphyrins by fluorimetry.[12]
The most common method for detecting fecal occult blood is based on the detection of heme. In these methods, the pseudoperoxidase activity of heme liberates nascent oxygen from hydrogen peroxide.[13] The liberated oxygen oxidizes a chromogen. Historically used chromagens are benzedrine and o-toluidine; these methods are sensitive, but benzedrine and toluidine are carcinogenic and are no longer used in clinical laboratories. Other chromogens used in this type of test are imipramine hydrochloride and desipramine hydrochloride.[6] The most common chromogen used today is guaiac, a natural resin extracted from Guaiacum officinale.[14] The sensitivity of the guaiac method is less than that based on o-toluidine. By employing a stabilizer, the sensitivity of the method has been improved.[15]
These tests consist of a card containing a high-quality filter paper impregnated with guaiac. This is stable for long periods because the guaiac is not in solution.[16] The developing solution is stabilized hydrogen peroxide in an aqueous alcoholic solution. Hemoglobin and its iron-containing degradation products, due to the pseudoperoxidase activity, release oxygen from hydrogen peroxide. The oxygen then oxidizes alpha-guaiaconic acid, a phenolic compound present in guaiac.[17] A quinine structure is formed, rearranging to a blue dye by internal electron transfer.[14]
The immunological methods are more specific and use antibodies against one of the components in blood, most commonly against the globin chain of the hemoglobin.[18] Hemoglobin forms a complex with a conjugate of an antibody to hemoglobin. The conjugate consists of a monoclonal or polyclonal antibody attached to a dye or enzyme, which will produce a colored product from the substrate present in the system.[19] A variety of immunochemical detection systems have been described. These include enzyme immunoassays (EIA), hemagglutination, latex agglutination, and colloidal gold agglutination assay.[20]
Many commercial kits have been developed for detecting blood by immunochemical methods, some of which are automated and therefore are more reproducible.[18][21] Immunochemical methods can be performed as a point-of-care method at the bedside by a healthcare professional, by the patient, or in the laboratory.[22]
Immunochemical methods do not require dietary restriction. Immunochemical methods are also more sensitive; the detection limits are lower than the guaiac-based methods.[19] With automated systems, reproducibility is increased further as the subjective nature of the visual reading of a result is removed. These methods can detect as little as 0.3 mL of blood added to stool.[21] These methods are also more specific for blood from the lower gastrointestinal tract, especially the colon; the globin released from hemoglobin in the upper gastrointestinal tract is hydrolyzed by proteolytic enzymes.[20]
In one device, a combination of immunological and guaiac-based tests is used. Hemoglobin is immobilized by a monoclonal antibody, and the hemoglobin is then visualized by the guaiac-based reaction. Non-hemoglobin peroxidases will give a background blue color, which is discounted.[23]
The heme-porphyrin test is based on the fact that the heme in the hemoglobin entering the gastrointestinal tract is converted to porphyrins, probably by gut bacteria. In this method, porphyrins in the feces are extracted and then quantitated by spectrofluorimetry.[24] This allows exact quantitation of the hemoglobin entering the gastrointestinal tract. This method is better at detecting bleeding in the upper gastrointestinal tract.[25] Guaiac and immunological methods are unreliable in detecting upper gastrointestinal tract bleeding because the hemoglobin may be digested by proteolytic enzymes in the gut.[26]
Recently a method using matrix-assisted laser desorption ionization/time of flight mass spectrometry (MALDI-TOF-MS) has been described. In this method, the fecal sample is mixed with water, ultrasonicated, and after centrifugation, the supernatant is combined with a matrix solution and used for MALDI-TOF-MS.[27] Blood is detected by identifying the water-soluble alpha and beta globin chains. This method is 10 to 100 times more sensitive than conventional methods, and there is no interference from plant peroxidases or dietary red meat.[28] The application of this method for routine use or screening has not been shown. This instrument is expensive; despite its many advantages, it may not be practical to use in clinical laboratories. The sensitivity (lower detection limit) of this method is 0.01 mg/g feces.[27]
Indications
The most common indications for FOBT are anemia, concern for gastrointestinal bleeding, and colon cancer screening. It can also be used to help discriminate irritable bowel syndrome (IBS) from inflammatory bowel disease (IBD), which is more likely to yield a positive test result. [9]
Potential Diagnosis
Occult fecal blood can be present secondary to several etiologies, some of which will be mentioned here. Neoplastic causes include adenocarcinoma, gastrointestinal metastasis, lymphoma, and leiomyosarcoma.[29] Inflammatory causes include Crohn disease, ulcerative colitis, gastritis, peptic ulcer disease, and diverticular bleeding.[30] Vascular causes include angiodysplasia, venous ectasia, variceal bleeding, hemangioma, gastric antral vascular ectasia, and a Dieulafoy lesion.[31] Infectious causes include salmonellae, enteroinvasive and enterohemorrhagic Escherichia coli, shigellae, neisseriae, yersiniae, Mycobacterium tuberculosis, campylobacterioses, and Strongyloides infections.[32]
Normal and Critical Findings
An FOBT card that does not turn blue is considered a negative test. If the card turns blue, this is positive and requires further gastroenterological workup.[13]
Normal fecal blood loss can approach 1.5 mL of blood per day based on radio chromium (51Cr-labeled red cells) methods.[33] In patients with benign adenomas or carcinoma of the large bowel, bleeding is often microscopic but, even so, can be in excess of 1.5 mL per day.[34] However, bleeding can be intermittent. Thus it is not always possible to distinguish normal from pathological bleeding by measuring fecal blood loss.[35] Furthermore, the amount of blood loss from tumors can vary daily, and there is non-uniform distribution of hemoglobin and its products in the feces.[36][37]
Peptic ulcers, hemorrhoids, and diverticula are also causes of fecal occult blood loss; bleeding from these conditions is highly variable. Of all the methods available, heme-porphyrin testing is more likely to detect small amounts of blood loss from the upper gastrointestinal tract, such as that seen due to aspirin.[38]
FOBT is performed to detect gastrointestinal bleeding and is most often used as a screening test for colorectal cancer, one of the most common cancers in many parts of the world.[3] There have been many studies on using fecal occult blood testing for the early detection of colorectal cancer.[13]
FOBT is also a critical investigation in patients with iron-deficiency anemia to rule out gastrointestinal bleeding as the cause of anemia. Since bleeding from any part of the gastrointestinal tract can cause iron deficiency, it is important to select the appropriate test.[39] Testing based on guaiac or immunological methods is less likely to detect upper gastrointestinal tract bleeding; heme-porphyrin testing is better at detecting upper gastrointestinal tract bleeding and can detect 90% of upper gastrointestinal tract bleeding. As little as 5 mL of blood loss per day can be detected.[40]
Interfering Factors
Fecal occult blood testing requires medication and dietary restrictions before testing. These restrictions decrease the risk of false-negative and false-positive results.[41] Many studies assessing the risk of these false results exist. One retrospective study evaluated the medications that could create false-positive results and encouraged patients to avoid these medications, if possible, for seven days before testing.[42] The listed medications include acetylsalicylic acid, unfractionated or low-molecular-weight heparin, warfarin, clopidogrel, nonsteroidal anti-inflammatory drugs, and selective serotonin reuptake inhibitors. The study found that 10.9% of the patients with positive FOBT and no dietary or medication restriction beforehand had normal follow-up endoscopic evaluations.[43]
Avoiding certain foods for three days before FOBT should help prevent false test results.[3] Inappropriate collection in patients with hematuria or menses may also result in false-positive test results.[13]
Guaiac-based methods are prone to interference from many sources. One of these is plant peroxidases. Raw fruits and vegetables such as turnips, broccoli, horseradish, cauliflower, cantaloupe, parsnip, and red radish contain high concentrations of peroxidases.[44] These peroxidases are heme proteins and have the prosthetic group ferri-protoporphyrin IX (hemin) and cause false-positive results in guaiac-based tests. However, it has been shown that cooking vegetables at 100^oC for 20 minutes inactivates plant peroxidase activity.[45]
Furthermore, gastric acid denatures peroxidase, so ingesting raw vegetables should not be problematic in patients with normal gastric acid secretion.[46] Ingestion of 750 g of raw, peroxidase-rich fruit and vegetables daily can cause false-positive results; this is an unusually large amount of vegetation to be eaten daily.[47] While delaying the development of the slide by 48 hours will reduce interferences from plant peroxidases, many manufacturers of guaiac-based tests recommend excluding high-peroxidase-containing fruits and vegetables before and during the collection of samples.[46]
Ingestion of red meat can cause false-positive results due to the peroxidase activity of heme in the meat.[48] The false-positive rate was higher when rehydration was used before the analysis.[35] Even after cooking the meat, some peroxidase activity can be detected.[44] Studies on healthy volunteers have shown that it takes about three days for the risk of a false-positive test due to meat ingestion to disappear.[49] While current recommendations are to avoid red meat for at least three days before testing, the time it takes for the risk of false-positive results to disappear after stopping red meat may vary in different clinical situations and with people with altered bowel movements. However, others have not found any significant effect of red meat on occult blood tests.[50]
A data meta-analysis concluded that dietary restriction might not be necessary for guaiac-based fecal occult blood tests.[51] Ascorbic acid (Vitamin C) can also negatively affect the oxidation of alpha-guaiaconic acid because vitamin C is a reducing agent. Ingestion of 1 to 2 grams of vitamin C daily can cause a false-negative result.[52] In-vitro studies suggest that a normal vitamin C intake will unlikely cause false-positive results.[53] A recent study found that consumption of 60 mg of vitamin C and 500 mL of orange juice (350 mg of vitamin C) produced variable results. In subjects taking high-dose supplements, false-negative results were seen.[54]
Using a povidone-iodine antiseptic solution is associated with false-positive results with guaiac-based assays.[55] In-vitro studies showed that as little as 0.005 mL of 1:1000 dilution of this solution would give a false-positive result. This interference is due to the iodine in the antiseptic causing oxidation of the alpha-guaiaconic acid.[56]
Using such antiseptic solutions on the perianal area or during urinary catheterization should be avoided before FOBT using guaiac methods. Drugs such as aspirin, other anti-inflammatory medications such as ibuprofen, naproxen, corticosteroids, or phenylbutazone, cancer chemotherapeutic agents, and alcohol in excess can all cause a positive reaction due to loss of blood from gastric irritation. Recent studies, however, suggest that low-dose aspirin does not affect the test.[57] In comparing subjects taking aspirin or other anti-inflammatory medications with those who are not, no difference in the rate of positive FOBT results was found. Therefore, avoiding these drugs before fecal occult blood testing may not be necessary.[58] Toilet sanitizers may cause false-positive results. Chlorine-generating sanitizers will give false-positive results with guaiac methods.[59] Nonchlorine-generating sanitizers reduce the immunological detection of hemoglobin.[60]
Complications
There are no known major complications of fecal occult blood testing.
Patient Safety and Education
The fecal occult blood test results are primarily affected by how patients prepare for the test, so it is important to follow the instructions carefully. Because certain foods can alter the test results, a special diet is often recommended for 48 to 72 hours before the test. In addition, patients should avoid drugs like anticoagulants, aspirin, colchicine, nonsteroidal antiarthritics, iron preparations, and steroids for at least seven days before the test.
Clinical Significance
Colorectal cancer is the third leading cause of cancer death for both genetic sexes. It occurs in all populations regardless of race, ethnicity, gender, or socioeconomic status.[61] It is most frequently diagnosed among persons aged 65 to 74 years. The absence of appropriate screening leads to the delay of both diagnosis and treatment.[62] FOBT is one of many methods used for colon cancer screening, and its use is valid in asymptomatic patients. It helps improve the detection of early-stage cancers by guiding patient selection for follow-up tests such as colonoscopies.[5] FOBT is unnecessary for high-risk or symptomatic patients, and these patients should promptly obtain a referral to a gastroenterologist for further workup and management.[6]
When misused or administered incorrectly, FOBT has resulted in unnecessary testing, increased healthcare costs, and prolonged hospital stays. Therefore, it should only be performed when indicated. Many organizations focus on educating healthcare providers about these indications.[9]
The US Preventive Services Task Force (USPSTF) concludes with high certainty that screening for colorectal cancer in adults aged 50 to 75 years has a substantial net benefit, and screening for colorectal cancer in adults aged 45 to 49 years has a moderate net benefit.[63] The USPSTF also concludes with moderate certainty that screening for colorectal cancer in adults aged 76 to 85 years who have been previously screened has a small net benefit. This assessment of net benefit applies to stool-based tests with high sensitivity, colonoscopy, computed tomography (CT) colonography, and flexible sigmoidoscopy.[64]
Colorectal cancer screening is now recommended for average-risk individuals starting at age 45, according to the American College of Gastroenterology guidelines.[65] In patients with first-degree relatives with advanced adenomas or colorectal carcinoma diagnosed before age 60, screening should begin at age 40 years or ten years earlier than the youngest diagnosed relative. In patients with first-degree relatives diagnosed with advanced adenomas or colorectal cancer after age 60, screening can begin at the usual age of 50.[66] Recommendations also exist that the fecal immunochemical test (FIT) replace the older guaiac-based FOBT due to increased sensitivity and specificity.[67] FIT targets human globin, often found with lower gastrointestinal bleeding, and it has been shown to improve detection rates for colorectal cancer compared to FOBT. It also does not necessitate any dietary modifications, improving patient adherence.[68]
References
Song LL, Li YM. Current noninvasive tests for colorectal cancer screening: An overview of colorectal cancer screening tests. World journal of gastrointestinal oncology. 2016 Nov 15:8(11):793-800 [PubMed PMID: 27895817]
Level 3 (low-level) evidenceSchreuders EH, Ruco A, Rabeneck L, Schoen RE, Sung JJ, Young GP, Kuipers EJ. Colorectal cancer screening: a global overview of existing programmes. Gut. 2015 Oct:64(10):1637-49. doi: 10.1136/gutjnl-2014-309086. Epub 2015 Jun 3 [PubMed PMID: 26041752]
Level 3 (low-level) evidenceMedical Advisory Secretariat. Fecal occult blood test for colorectal cancer screening: an evidence-based analysis. Ontario health technology assessment series. 2009:9(10):1-40 [PubMed PMID: 23074514]
Khakimov N, Khasanova G, Ershova K, Gibadullina L, Vetkina T, Lobisheva G, Chumakova A. Screening for colon cancer: A test for occult blood. The International journal of risk & safety in medicine. 2015:27 Suppl 1():S110-1. doi: 10.3233/JRS-150712. Epub [PubMed PMID: 26639687]
Li JN, Yuan SY. Fecal occult blood test in colorectal cancer screening. Journal of digestive diseases. 2019 Feb:20(2):62-64. doi: 10.1111/1751-2980.12712. Epub 2019 Mar 5 [PubMed PMID: 30714325]
Wielandt AM, Hurtado C, Moreno M, Zárate A, López-Köstner F. [Fecal occult blood test for colorectal cancer screening]. Revista medica de Chile. 2021 Apr:149(4):580-590. doi: 10.4067/s0034-98872021000400580. Epub [PubMed PMID: 34479346]
Thomas WM, Pye G, Hardcastle JD, Mangham CM. Faecal occult blood screening for colorectal neoplasia: a randomized trial of three days or six days of tests. The British journal of surgery. 1990 Mar:77(3):277-9 [PubMed PMID: 2322789]
Level 1 (high-level) evidenceElsafi SH, Alqahtani NI, Zakary NY, Al Zahrani EM. The sensitivity, specificity, predictive values, and likelihood ratios of fecal occult blood test for the detection of colorectal cancer in hospital settings. Clinical and experimental gastroenterology. 2015:8():279-84. doi: 10.2147/CEG.S86419. Epub 2015 Sep 9 [PubMed PMID: 26392783]
Sokoro A, Singh H. Fecal Occult Blood Test for Evaluation of Symptoms or for Diagnostic Testing. The American journal of gastroenterology. 2020 May:115(5):679-680. doi: 10.14309/ajg.0000000000000560. Epub [PubMed PMID: 32058343]
Young GP, Sinatra MA, St John DJ. Influence of delay in stool sampling on fecal occult blood test sensitivity. Clinical chemistry. 1996 Jul:42(7):1107-8 [PubMed PMID: 8674197]
Navarro M, Nicolas A, Ferrandez A, Lanas A. Colorectal cancer population screening programs worldwide in 2016: An update. World journal of gastroenterology. 2017 May 28:23(20):3632-3642. doi: 10.3748/wjg.v23.i20.3632. Epub [PubMed PMID: 28611516]
Kaur K, Adamski JJ. Fecal Occult Blood Test. StatPearls. 2023 Jan:(): [PubMed PMID: 30725823]
Lee MW, Pourmorady JS, Laine L. Use of Fecal Occult Blood Testing as a Diagnostic Tool for Clinical Indications: A Systematic Review and Meta-Analysis. The American journal of gastroenterology. 2020 May:115(5):662-670. doi: 10.14309/ajg.0000000000000495. Epub [PubMed PMID: 31972617]
Level 1 (high-level) evidenceShaukat A, Church TR, Mandel JS. Guaiac Fecal Occult Blood Test and Reduction in Colorectal Cancer Incidence. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association. 2021 Oct:19(10):2217. doi: 10.1016/j.cgh.2021.05.008. Epub 2021 May 6 [PubMed PMID: 33965576]
Park DI, Ryu S, Kim YH, Lee SH, Lee CK, Eun CS, Han DS. Comparison of guaiac-based and quantitative immunochemical fecal occult blood testing in a population at average risk undergoing colorectal cancer screening. The American journal of gastroenterology. 2010 Sep:105(9):2017-25. doi: 10.1038/ajg.2010.179. Epub 2010 May 25 [PubMed PMID: 20502450]
Greenwald B. From guaiac to immune fecal occult blood tests: the emergence of technology in colorectal cancer screening. Gastroenterology nursing : the official journal of the Society of Gastroenterology Nurses and Associates. 2005 Mar-Apr:28(2):90-6 [PubMed PMID: 15832108]
Wilkins T, McMechan D, Talukder A. Colorectal Cancer Screening and Prevention. American family physician. 2018 May 15:97(10):658-665 [PubMed PMID: 29763272]
Yuan SY, Wu W, Fu J, Lang YX, Li JC, Guo Y, Wang YN, Qian JM, Li JN. Quantitative immunochemical fecal occult blood test for neoplasia in colon cancer screening. Journal of digestive diseases. 2019 Feb:20(2):78-82. doi: 10.1111/1751-2980.12711. Epub 2019 Mar 10 [PubMed PMID: 30714346]
Level 2 (mid-level) evidenceOu CH, Kuo FC, Hsu WH, Lu CY, Yu FJ, Kuo CH, Wang JY, Wu MT, Shiea J, Wu DC, Hu HM. Comparison of the performance of guaiac-based and two immunochemical fecal occult blood tests for identifying advanced colorectal neoplasia in Taiwan. Journal of digestive diseases. 2013 Sep:14(9):474-83. doi: 10.1111/1751-2980.12077. Epub [PubMed PMID: 23701988]
Quintero E. [Chemical or immunological tests for the detection of fecal occult blood in colorectal cancer screening?]. Gastroenterologia y hepatologia. 2009 Oct:32(8):565-76. doi: 10.1016/j.gastrohep.2009.01.179. Epub 2009 Jul 3 [PubMed PMID: 19577340]
Level 2 (mid-level) evidenceVilkin A, Rozen P, Levi Z, Waked A, Maoz E, Birkenfeld S, Niv Y. Performance characteristics and evaluation of an automated-developed and quantitative, immunochemical, fecal occult blood screening test. The American journal of gastroenterology. 2005 Nov:100(11):2519-25 [PubMed PMID: 16279909]
Kościelniak-Merak B, Radosavljević B, Zając A, Tomasik PJ. Faecal Occult Blood Point-of-Care Tests. Journal of gastrointestinal cancer. 2018 Dec:49(4):402-405. doi: 10.1007/s12029-018-0169-1. Epub [PubMed PMID: 30232694]
Rabeneck L, Rumble RB, Thompson F, Mills M, Oleschuk C, Whibley A, Messersmith H, Lewis N. Fecal immunochemical tests compared with guaiac fecal occult blood tests for population-based colorectal cancer screening. Canadian journal of gastroenterology = Journal canadien de gastroenterologie. 2012 Mar:26(3):131-47 [PubMed PMID: 22408764]
Young GP, Cole SR. Which fecal occult blood test is best to screen for colorectal cancer? Nature clinical practice. Gastroenterology & hepatology. 2009 Mar:6(3):140-1. doi: 10.1038/ncpgasthep1358. Epub 2009 Jan 27 [PubMed PMID: 19174764]
Ahlquist DA, McGill DB, Schwartz S, Taylor WF, Owen RA. Fecal blood levels in health and disease. A study using HemoQuant. The New England journal of medicine. 1985 May 30:312(22):1422-8 [PubMed PMID: 3873009]
St John DJ, Young GP, Alexeyeff MA, Deacon MC, Cuthbertson AM, Macrae FA, Penfold JC. Evaluation of new occult blood tests for detection of colorectal neoplasia. Gastroenterology. 1993 Jun:104(6):1661-8 [PubMed PMID: 8500724]
Wu CI, Tsai CC, Lu CC, Wu PC, Wu DC, Lin SY, Shiea J. Diagnosis of occult blood in human feces using matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. Clinica chimica acta; international journal of clinical chemistry. 2007 Sep:384(1-2):86-92 [PubMed PMID: 17662705]
Lin SY, Shih SH, Wu DC, Lee YC, Wu CI, Lo LH, Shiea J. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the detection of hemoglobins as the protein biomarkers for fecal occult blood. Rapid communications in mass spectrometry : RCM. 2007:21(20):3311-6 [PubMed PMID: 17879387]
Simon JB. Fecal occult blood testing: clinical value and limitations. The Gastroenterologist. 1998 Mar:6(1):66-78 [PubMed PMID: 9531118]
Fu Y, Wang L, Xie C, Zou K, Tu L, Yan W, Hou X. Comparison of non-invasive biomarkers faecal BAFF, calprotectin and FOBT in discriminating IBS from IBD and evaluation of intestinal inflammation. Scientific reports. 2017 Jun 1:7(1):2669. doi: 10.1038/s41598-017-02835-5. Epub 2017 Jun 1 [PubMed PMID: 28572616]
Dalle I, Geboes K. Vascular lesions of the gastrointestinal tract. Acta gastro-enterologica Belgica. 2002 Oct-Dec:65(4):213-9 [PubMed PMID: 12619428]
Papaconstantinou HT, Thomas JS. Bacterial colitis. Clinics in colon and rectal surgery. 2007 Feb:20(1):18-27. doi: 10.1055/s-2007-970196. Epub [PubMed PMID: 20011357]
Moralidis E, Papanastassiou E, Arsos G, Chilidis I, Gerasimou G, Gotzamani-Psarrakou A. A single measurement with (51)Cr-tagged red cells or (125)I-labeled human serum albumin in the prediction of fractional and whole blood volumes: an assessment of the limitations. Physiological measurement. 2009 Jul:30(7):559-71. doi: 10.1088/0967-3334/30/7/003. Epub 2009 May 21 [PubMed PMID: 19458409]
Pineda AA, Dharkar DD, Wahner HW. Clinical evaluation of a 51Cr-labeled red blood cell survival test for in vivo blood compatibility testing. Mayo Clinic proceedings. 1984 Jan:59(1):25-30 [PubMed PMID: 6694429]
Macrae FA, St John DJ, Caligiore P, Taylor LS, Legge JW. Optimal dietary conditions for hemoccult testing. Gastroenterology. 1982 May:82(5 Pt 1):899-903 [PubMed PMID: 7060911]
St John DJ, Young GP, McHutchison JG, Deacon MC, Alexeyeff MA. Comparison of the specificity and sensitivity of Hemoccult and HemoQuant in screening for colorectal neoplasia. Annals of internal medicine. 1992 Sep 1:117(5):376-82 [PubMed PMID: 1503328]
Level 2 (mid-level) evidenceRosenfield RE, Kochwa S, Kaczera Z, Maimon J. Nonuniform distribution of occult blood in feces. American journal of clinical pathology. 1979 Feb:71(2):204-9 [PubMed PMID: 106720]
Lynch NM, McHutchison JG, Young GP, Deacon M, St John DJ, Barraclough D. Gastrointestinal blood loss from a new buffered aspirin (Ostoprin): measurement by radiochromium and Hemoquant techniques. Australian and New Zealand journal of medicine. 1989 Apr:19(2):89-96 [PubMed PMID: 2788406]
Level 1 (high-level) evidenceChowdhury ATMD, Longcroft-Wheaton G, Davis A, Massey D, Goggin P. Role of faecal occult bloods in the diagnosis of iron deficiency anaemia. Frontline gastroenterology. 2014 Oct:5(4):231-236. doi: 10.1136/flgastro-2013-100425. Epub 2014 Jan 27 [PubMed PMID: 28839778]
Harewood GC, McConnell JP, Harrington JJ, Mahoney DW, Ahlquist DA. Detection of occult upper gastrointestinal tract bleeding: performance differences in fecal occult blood tests. Mayo Clinic proceedings. 2002 Jan:77(1):23-8 [PubMed PMID: 11794453]
Level 2 (mid-level) evidenceWong C, Dubé C. More on fecal occult blood test misuse. Canadian journal of gastroenterology & hepatology. 2014 Sep:28(8):419-20 [PubMed PMID: 25229464]
Konrad G, Katz A. Are medication restrictions before FOBT necessary?: practical advice based on a systematic review of the literature. Canadian family physician Medecin de famille canadien. 2012 Sep:58(9):939-48 [PubMed PMID: 22972722]
Level 1 (high-level) evidenceNarula N, Ulic D, Al-Dabbagh R, Ibrahim A, Mansour M, Balion C, Marshall JK. Fecal occult blood testing as a diagnostic test in symptomatic patients is not useful: a retrospective chart review. Canadian journal of gastroenterology & hepatology. 2014 Sep:28(8):421-6 [PubMed PMID: 25014182]
Level 2 (mid-level) evidenceCaligiore P, Macrae FA, St John DJ, Rayner LJ, Legge JW. Peroxidase levels in food: relevance to colorectal cancer screening. The American journal of clinical nutrition. 1982 Jun:35(6):1487-9 [PubMed PMID: 7081130]
Griffith CD, Turner DJ, Saunders JH. False-negative results of Hemoccult test in colorectal cancer. British medical journal (Clinical research ed.). 1981 Aug 15:283(6289):472 [PubMed PMID: 6790022]
Meyer GW, Komadina K, Perucca P. Vegetable peroxidase is denatured by gastric acid: fresh vegetables do not cause false-positive stool Hemoccults in normal subjects. Gastroenterology. 1991 Sep:101(3):871 [PubMed PMID: 1650322]
Level 3 (low-level) evidenceZwillenberg LO. [Prevention of false results in tests for occult blood in feces]. Schweizerische Rundschau fur Medizin Praxis = Revue suisse de medecine Praxis. 1990 Apr 24:79(17):521-3 [PubMed PMID: 2187220]
Sinatra MA, St John DJ, Young GP. Interference of plant peroxidases with guaiac-based fecal occult blood tests is avoidable. Clinical chemistry. 1999 Jan:45(1):123-6 [PubMed PMID: 9895348]
Feinberg EJ, Steinberg WM, Banks BL, Henry JP. How long to abstain from eating red meat before fecal occult blood tests. Annals of internal medicine. 1990 Sep 1:113(5):403-4 [PubMed PMID: 2200323]
Level 3 (low-level) evidenceNorfleet RG. Effect of diet on fecal occult blood testing in patients with colorectal polyps. Digestive diseases and sciences. 1986 May:31(5):498-501 [PubMed PMID: 3009111]
Level 3 (low-level) evidencePignone M, Campbell MK, Carr C, Phillips C. Meta-analysis of dietary restriction during fecal occult blood testing. Effective clinical practice : ECP. 2001 Jul-Aug:4(4):150-6 [PubMed PMID: 11525101]
Level 1 (high-level) evidenceJaffe RM, Kasten B, Young DS, MacLowry JD. False-negative stool occult blood tests caused by ingestion of ascorbic acid (vitamin C). Annals of internal medicine. 1975 Dec:83(6):824-6 [PubMed PMID: 1200528]
Garrick DP, Close JR, McMurray W. Detection of occult blood in faeces. Lancet (London, England). 1977 Oct 15:2(8042):820-1 [PubMed PMID: 71626]
Level 3 (low-level) evidenceFranke AA, Cooney RV, Henning SM, Custer LJ. Bioavailability and antioxidant effects of orange juice components in humans. Journal of agricultural and food chemistry. 2005 Jun 29:53(13):5170-8 [PubMed PMID: 15969493]
Blebea J, McPherson RA. False-positive guaiac testing with iodine. Archives of pathology & laboratory medicine. 1985 May:109(5):437-40 [PubMed PMID: 3838658]
Level 3 (low-level) evidenceHait WN, Snepar R, Rothmen C. False-positive hematest due to povidone-iodine. The New England journal of medicine. 1977 Dec 15:297(24):1350-1 [PubMed PMID: 917095]
Level 3 (low-level) evidenceGreenberg PD, Cello JP, Rockey DC. Relationship of low-dose aspirin to GI injury and occult bleeding: a pilot study. Gastrointestinal endoscopy. 1999 Nov:50(5):618-22 [PubMed PMID: 10536315]
Level 3 (low-level) evidenceKahi CJ, Imperiale TF. Do aspirin and nonsteroidal anti-inflammatory drugs cause false-positive fecal occult blood test results? A prospective study in a cohort of veterans. The American journal of medicine. 2004 Dec 1:117(11):837-41 [PubMed PMID: 15589487]
Level 2 (mid-level) evidenceAhlquist DA, Schwartz S, Isaacson J, Ellefson M. A stool collection device: the first step in occult blood testing. Annals of internal medicine. 1988 Apr:108(4):609-12 [PubMed PMID: 3348567]
Imafuku Y, Nagai T, Yoshida H. The effect of toilet sanitizers and detergents on immunological occult blood tests. Clinica chimica acta; international journal of clinical chemistry. 1996 Sep 30:253(1-2):51-9 [PubMed PMID: 8879838]
Rawla P, Sunkara T, Barsouk A. Epidemiology of colorectal cancer: incidence, mortality, survival, and risk factors. Przeglad gastroenterologiczny. 2019:14(2):89-103. doi: 10.5114/pg.2018.81072. Epub 2019 Jan 6 [PubMed PMID: 31616522]
Petre-Mandache CB, Margaritescu DN, Mitrut R, Kamal AM, Padureanu V, Cucu MG, Mitrut P. Risk Factors and Genetic Predisposition in Colorectal Cancer: A Study on Young and Old Adults. Current health sciences journal. 2021 Jan-Mar:47(1):84-88. doi: 10.12865/CHSJ.47.01.13. Epub 2021 Mar 31 [PubMed PMID: 34211752]
US Preventive Services Task Force, Davidson KW, Barry MJ, Mangione CM, Cabana M, Caughey AB, Davis EM, Donahue KE, Doubeni CA, Krist AH, Kubik M, Li L, Ogedegbe G, Owens DK, Pbert L, Silverstein M, Stevermer J, Tseng CW, Wong JB. Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 2021 May 18:325(19):1965-1977. doi: 10.1001/jama.2021.6238. Epub [PubMed PMID: 34003218]
Ng K, May FP, Schrag D. US Preventive Services Task Force Recommendations for Colorectal Cancer Screening: Forty-Five Is the New Fifty. JAMA. 2021 May 18:325(19):1943-1945. doi: 10.1001/jama.2021.4133. Epub [PubMed PMID: 34003238]
de Kanter C, Dhaliwal S, Hawks M. Colorectal Cancer Screening: Updated Guidelines From the American College of Gastroenterology. American family physician. 2022 Mar 1:105(3):327-329 [PubMed PMID: 35289558]
Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK. ACG Clinical Guidelines: Colorectal Cancer Screening 2021. The American journal of gastroenterology. 2021 Mar 1:116(3):458-479. doi: 10.14309/ajg.0000000000001122. Epub [PubMed PMID: 33657038]
Day LW, Bhuket T, Allison J. FIT testing: an overview. Current gastroenterology reports. 2013 Nov:15(11):357. doi: 10.1007/s11894-013-0357-x. Epub [PubMed PMID: 24218070]
Level 3 (low-level) evidenceTinmouth J, Lansdorp-Vogelaar I, Allison JE. Faecal immunochemical tests versus guaiac faecal occult blood tests: what clinicians and colorectal cancer screening programme organisers need to know. Gut. 2015 Aug:64(8):1327-37. doi: 10.1136/gutjnl-2014-308074. Epub 2015 Jun 3 [PubMed PMID: 26041750]