Synonym

• Fecal occult blood
• FOBT
• gFOBT
• Guaiac smear test
• Hemoccult
• IFOBT
• Immunoassay fecal occult blood test
• Immunoassay FOBT
• Immunochemical fecal occult blood test
• Stool occult blood

Tubes

• Random stool (feces) specimen
• Submit 5g (2 ml) of stool (container provided by lab)

Or

• Fecal sample applied in the circle on card or slide (provided by lab)

Additional information

• Stool collection:
• Clear instructions should be communicated and given in writing to the patient to ensure proper collection
• Instruct the patient to defecate in a large-mouthed plastic container, bag, or clean bedpan
• Wear gloves, collect the required amount of specimen and transfer it to a container using a clean tongue blade or similar object
• Collect a very small stool specimen on the tip of a wooden applicator, and apply thin smear of specimen inside the circle of the card provided
• Close cover and dispose the applicator
• Provide for and respect the patient's privacy
• The patient is instructed to consume a high-residue diet (raw and cooked carrots, corn, or spinach, prunes, bran cereals, peanuts, and popcorn), 72 hrs prior to the test and continue throughout the collection period
• Avoid the following, 2-3 days prior to the test
• Vegetables and fruits such as turnips, horseradish, beets, radishes,artichokes, cauliflower, broccoli, cantaloupe, parsnips, mushrooms, bean sprouts, bananas, apples, oranges, grapes, and melon
• Red meat such as beef, lamb, processed meat, liver
• Iron and vitamin C supplements
• Alcohol, aspirin, steroids, non-steroidal anti-inflammatory drugs (for 7 days prior to the test)
• Medications such as colchicine, iodine, antacids, or boric acid
• Laxative, barium sulfate, mineral oil, bismuth, antidiarrheal therapy or antiparasitic therapy (for 2 wks prior to the test)
• Empty bladder completely to avoid contamination with urine
• Avoid sample collection at or until 3 days after menstrual period, bleeding hemorrhoids or presence of blood in urine
• Label the samples properly including date and time of the collection of stool
• Protect card or slide from light, heat, humidity, and volatile chemicals (e.g., iodine, bleach)
• Send the specimen to lab immediately (or apply reagent at bedside if trained to do so) and do not refrigerate
• 3-6 separate random stool specimens preferred if using to screen for colon cancer

Info

• Fecal occult blood test is a noninvasive test to detect the presence of hidden (occult) blood in the stool
• A healthy person passes up to 2-2.5 mL of blood per 150 g of stool into the gastrointestinal tract per day. Passage of more than 2 mL of blood in the stool in 24 hrs is pathologically significant
• Fecal occult blood test is detected by various methods:
• Chemical methods, such as Hematest and Hemoccult
• Fecal porphyrin quantification (HemoQuant test)
• Immunochemical methods such as HemeSelect and QuickVue iFOB test
• Microscopic analysis
• Fecal DNA test (PreGen-Plus)
• Hemoccult test is most widely used and is a guaiac-based test. The heme moiety of hemoglobin in the fecal sample has pseudoperoxidase activity that catalyzes the oxidation of guaiac by hydrogen peroxide to produce a blue color

Clinical

• The clinical utility of fecal occult blood testing includes:
• Aids in diagnosing gastrointestinal (GI) disorders by detection of gastrointestinal bleeding such as colon cancer, hemorrhoids, anal fissure, colon polyps, gastric ulcer etc.
• As a routine screening test in persons >50 yrs of age for early diagnosis of colorectal cancer (recommended by the American Cancer Society)
• Evaluation of persons presenting with abdominal pain
• Evaluation of cause of anemia
• Detection of GI bleeding due to drug therapy
• Smaller amount of blood in the stool is not visible but detectable by chemical assays so as to detect and treat gastrointestinal disease early in its course
• Dark red/maroon to tarry black appearing stool is most consistent with loss of >50–75 mL of blood from the upper GI tract
• Overtly bloody stool is most consistent with bleeding in the lower GI tract (can occur with very rapid upper GI bleeding)
• It is estimated that 2-10% have colorectal or gastric cancer and 20-30% have adenomas or polyps in positive occult blood test
• Though the sensitivity and specificity of FOBT is low in detecting colon cancer, as a screening test can reduce mortality rates from colorectal cancer by 30-40% (National Cancer Institute)
• The advantages of FOBT includes:
• Convenient
• Noninvasive
• Poses no physical risks
• Relatively inexpensive
• Colon preparation not required
• Samples can be taken at home
• No risk of bleeding or tears in colon lining
• Annual FOBT covered by Medicare for those over age of 50
• The disadvantages of FOBT includes:
• Nonspecific – blood that appears could have come from any source
• Interaction with food and medicine can lead to erroneous results
• Detects blood only when bleeding occurs, some tumors do not bleed or bleed intermittently
• May fail to detect polyps or cancers (high false negative rate)
• When the result is positive, additional procedures then are necessary to detect cause of bleeding

Additional information

• Fecal occult blood test results are accurate if patient preparation and collection of specimen are followed explicitly
• Guaiac-based test (Hemoccult) is the most widely used test for stool occult blood in U.S. This is probably because it is rapid, office-based, and inexpensive, with a false positive rate of 1-12%
• Fecal porphyrin quantification (HemoQuant) has a high false positive rate, is expensive, requires laboratory time, but has the advantage of dietary peroxidases not affected test results
• Immunochemical methods (HemeSelect, QuickVue iFOB) are more specific and sensitive to lower GI bleeding as they detect intact hemoglobin (consumption of red meat or dietary peroxidases do not produce false-positive results). Disadvantages are limited availability, long lab processing time, and an inability to detect digested hemoglobin especially from the upper GI bleeding
• The stool-based DNA test (PreGen-Plus) is more sensitive and specific; especially in early detection of colorectal cancer in otherwise healthy adults
• Factors interfering with test results include
• Bleeding hemorrhoids (take samples from center of stool to avoid this error)
• Collection of specimen during menstrual period
• Hematuria
• Contamination with toilet bowl cleansers
• Failure to observe pretest restrictions
• Ingestion of 2–5 ml of blood such as from bleeding gums
• Related laboratory tests include:
• Complete blood count
• Colonoscopy
• Intestinal biopsy
• Stool culture
• Stool ova and parasites

Nl Result

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

• Normal: Negative for blood

High Result

• Upper gastrointestinal bleeding (esophagus/stomach)
• Esophagitis
• Gastritis
• Gastric ulcer
• Esophageal varices
• Mallory-Weiss tear
• Gastrointestinal malignancy
• Dieulafoy's lesion
• Portal gastropathy
• Gastric antral vascular ectasia
• Arteriovenous malformation
• Angiodysplasia
• Bleeding from small intestine
• Duodenitis
• Duodenal ulcer
• Celiac sprue
• Meckel's diverticulum
• Crohn's disease
• Gluten enteropathy
• Lower gastrointestinal bleeding
• Diverticulitis
• Ischemic colitis
• Inflammatory bowel disease
• Ulcerative colitis
• Pseudomembranous colitis
• Infections
• Amebiasis
• Ascariasis
• Cytomegalovirus
• Hookworm
• Strongyloides
• Tuberculous enterocolitis
• Whipworm
• Colon cancer
• Rectal cancer
• Colorectal polyps
• Hemorrhoids
• Anal fissure
• Arteriovenous malformations
• Colonic stricture
• Any gastrointestinal source
• Vascular ectasia/angiodysplasia (3-12%)
• Vasculitis
• Aortoenteric fistula
• Other cancers
• Carcinoid tumors
• Kaposi's sarcoma
• Leiomyoma
• Leiomyosarcoma
• Lymphoma
• Melanoma
• Telangiectasia (Osler-Weber-Rendu syndrome)
• Blue rubber bleb nevus syndrome
• Amyloidosis
• Hemangioma
• Radiation-induced mucosal injury
• Extraintestinal source
• Hemobilia
• Hemosuccus pancreaticus
• Hemorrhagic disease
• Hemoptysis
• Nasopharyngeal (epistaxis, bleeding gums)
• Factitious
• Long-distance running
• Drugs
• Acetylsalicylic acid
• Anticoagulants
• Antimetabolites
• Colchicines
• Corticosteroids
• Indomethacin
• Iron preparations
• NSAIDs
• Phenylbutazone
• Salicylates (aspirin)

Conditions and substances associated with false positive test results include:

• Red meats such as processed meats and liver
• Vegetables and fruits (with peroxidase activity) such as turnips, horseradish, beets, radishes,artichokes, cauliflower, broccoli, cantaloupe, parsnips, mushrooms, bean sprouts, bananas, apples, oranges, grapes, and melon
• Drug
• Boric acid
• Bromides
• Colchicine
• Iodine
• Povidone-iodine (Betadine)

References

• Fraser SG et al. Evaluation of a card collection based faecal immunochemical test in screening for colorectal cancer using a two-tier reflex approach. Gut. 2007 Feb 19; [Epub ahead of print]
• Imperiale TF et al. Fecal DNA versus fecal occult blood for colorectal-cancer screening in an average-risk population. N Engl J Med. 2004 Dec 23;351(26):2704-14.
• Laboratory Corporation of America. Occult Blood, Stool, Guaiac. [Homepage on the internet]©2007. Last updated on February 27, 2007. Last accessed on April 4, 2007. Available at URL: http://www.labcorp.com/datasets/labcorp/html/chapter/mono/mb010300.htm
• LabTestsOnline®. Fecal Occult Blood Test. [Homepage on the Internet]©2001-2007. Last reviewed on July 6, 2005. Last accessed on April 4, 2007. Available at URL: http://www.labtestsonline.org/understanding/analytes/fecal_occult_blood/glance.html
• Levi Z et al. A quantitative immunochemical fecal occult blood test for colorectal neoplasia. Ann Intern Med. 2007 Feb 20;146(4):244-55.
• Mitchell SH et al. A new view of occult and obscure gastrointestinal bleeding. Am Fam Physician. 2004 Feb 15;69(4):875-81. Available at URL: http://www.aafp.org/afp/20040215/875.html
• Peterson MB et al. Colorectal cancer screening among men and women in the United States. J Womens Health (Larchmt). 2007 Jan-Feb;16(1):57-65.
• UTMB Laboratory Survival Guide®. OCCULT BLOOD, feces. [Homepage on the Internet]© 2006. Last reviewed on February 1, 2004. Last accessed on April 4, 2007. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/micro/OCCULT%20BLOOD%20feces.html