Synonym
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 >5075 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 25 ml of blood such as from bleeding gums
- Related laboratory tests include:
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