Occult Blood, Stool, Guaiac

Occult Blood, Stool, Guaiac

Number
	008607
CPT
	82272
Synonyms
	Blood, Occult, Stool ; Hemoccult®
Specimen
	Card with stool smear or stool
Volume
	Card with thin stool smear or 5 g stool
Container
	Collection card or stool transport vial without preservative (ParaPak white clean vial)
Storage Instructions
	Maintain card at room temperature. Refrigerate or freeze stool transport vial.
Patient Preparation
	Patient should not receive vitamin C (ascorbic acid) for 3 days prior to occult blood testing by guaiac. A high bulk, red meat free diet with restriction of peroxidase-rich vegetables (turnips, horseradish, artichokes, mushrooms, radishes, broccoli, bean sprouts, cauliflower, oranges, bananas, cantaloupes, grapes), has been recommended for 72 hours prior to guaiac testing, and during testing, to decrease the incidence of false-positives. Therapeutic iron causes false-positives with guaiac tests in more than half of healthy subjects.
Causes for Rejection
	Inappropriate specimen transport device; unlabeled specimen or name discrepancy between specimen and request label; specimen received after prolonged delay (usually more than 14 days if card is received); expired transport device
Use
	Detect occult blood
Limitations
	Most methods lack sensitivity to small amounts of blood and might fail to detect slow rates of blood loss. When occult GI bleeding is suspected, at least three samples, from separate bowel movements, should be submitted. Many substances and conditions interfere with guaiac tests. Vitamin C (ascorbic acid) and antacids may cause false-negatives to guaiac tests. False-positive results may be caused by excessive dietary intake of vegetable peroxidases, especially horseradish. Drugs shown to be associated with gastrointestinal blood loss in normal subjects include salicylates (aspirin), steroids, rauwolfia derivatives, all nonsteroidal anti-inflammatory drugs, and colchicine. The sensitivity of the slides is increased by rehydration prior to development; however, this increases the rate of false-positives. The increment in sensitivity provided by rehydration can be a useful adjunct to the use of the test,¹ but may significantly decrease its specificity. Guaiac tests present a number of other problems. Acid pH, heat, and dry stools lead to some false-negatives, while watery stools are more apt to test positive. Intestinal converted fraction is an expression that describes the fraction of heme converted to porphyrin during fecal transit, a phenomenon that leads to diminished guaiac sensitivity for carcinomas of the more proximal colon.^2,3,4
Methodology
	Guaiac is a leuko-dye. More commercially generated tests are based on it. The peroxidase-like activity of hemoglobin or nonspecific oxidants catalyzes the reaction of peroxide and the chromogen orthotolidine to form blue oxidized orthotolidine.
Additional Information
	Methods for guaiac tests of stool for occult blood use peroxidation of a chromogen by stool peroxidases. Hemoglobin acts as a peroxidase, but stool may also contain meat, bacterial and plant peroxidases. Normal intestinal blood loss averages 2-2.5 mL. Commercially available guaiac assays will begin to turn positive at about 5 mg hemoglobin per gram of stool, which is considered to be the upper limit of normal stool peroxidase activity. This method is capable of detection of 6 mg of added hemoglobin per gram of feces in 90% of observations, but will fail 80% of the time to detect up to 1.5 mg/g of feces. After ingestion of 8 oz of cooked red meat per day, reactions remain negative 95% of the time.
Footnotes
	Macrae FA, St John DJ, Caligiore P, et al, “Optimal Dietary Conditions for Hemoccult® Testing,” Gastroenterology, 1982, 82(5 Pt 1):899-903. Ahlquist DA and Bakken CL, “Fecal Blood Tests,” ASCP Check Sample®, Chicago, IL: American Society of Clinical Pathologists, 1988. Ahlquist DA, McGill DB, Schwartz S, et al, “Fecal Blood Levels in Health and Disease,” N Engl J Med, 1985, 312(22):1422-8. Selby JV, Friedman GD, Quesenberry CP Jr, et al, “Effect of Fecal Occult Blood Testing on Mortality From Colorectal Cancer. A Case-Control Study,” Ann Intern Med, 1993, 118(1):1-6
References
	Bahrt KM, Korman LY, and Nashel DJ, “Significance of a Positive Test for Occult Blood in Stools of Patients Taking Anti-inflammatory Drugs,” Arch Intern Med, 1984, 144(11):2165-6. Blebea J and McPherson RA, “False-Positive Guaiac Testing With Iodine,” Arch Pathol Lab Med, 1985, 109(5):437-40. Block GE, “Colon Cancer: Diagnosis and Prognosis in the Elderly,” Geriatrics, 1989, 44(5):45-7, 52-3. Doyle AC, “A Study in Scarlet,” Philadelphia, PA: JB Lippincott Co, 1902. Fleischer DE, Goldberg SB, Browning TH, et al, “Detection and Surveillance of Colorectal Cancer,” JAMA, 1989, 261(4):580-5. Gambino R, “Occult Blood Screening for Colorectal Carcinoma,” Lab Report for Physicians, 1986, 8:49-53. Klos SE, Drinka P, and Goodwin JS, “The Utilization of Fecal Occult Blood Testing in the Institutionalized Elderly,” J Am Geriatr Soc, 1991, 39(12):1169-73. Knight KK, Fielding JE, and Battista RN, “US Preventive Services Task Force. Occult Blood Screening for Colorectal Cancer,” JAMA, 1989, 261(4):587-93. Losek JD and Fiete RL, “Intussusception and the Diagnostic Value of Testing Stool for Occult Blood,” Am J Emerg Med, 1991, 9(1):1-3. Pye G, Jackson J, Thomas WM, et al, “Comparison of ColoScreen Self-Test and Haemoccult Faecal Occult Blood Tests in the Detection of Colorectal Cancer in Symptomatic Patients,” Br J Surg, 1990, 77(6):630-1.