Fecal Occult Blood

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Contents 1 More Specific Terms 2 Introduction 3 Indications 4 Procedure 5 Interferences 6 Differential-diagnosis 7 Management 8 More General Terms 9 Additional Terms 10 References

More Specific Terms

• stool guaiac

Introduction

• Detection of traces of blood in the feces too small to be seen.

Indications

• screening for colon cancer
• evaluation of anemia
• evaluation of gastrointestinal hemorrhage

• abdominal pain
• changes in bowel movements
• weight loss
• melena

Procedure

• The stool Guaiac test assesses peroxidase activity by addition of hydrogen peroxide to guaiac, orthotoluidine, orthodinisidine or benzidine. Guaiac is the most commonly used, & the least sensitive reagent resulting in formation of a blue color with peroxidase activity. Peroxidase activity results most commonly from the presence of hemoglobin.
  
• Newer tests, iFOBT, ColonCARE, Hemoccult, ICT, InSure, use antibody to hemoglobin (immnunochemical FOBT, iFOBT)
• Sensitivity of iFOBT for detecting advanced neolasia is 44% vs 17% for Guaiac based methods [11]
• Specificities of iFOBT & Guaiac based methods are similar (92% vs. 93%)
• Fewer colonoscopies are necessary to detect colon cancer with iFOBT than with Guaiac based methods [11]
• Quantitative immunochemical testing holds promise [7,8]
  
• Normal individuals lose 2.0-2.5 mL of blood into the gastrointestinal tract daily. Guaiac test kits detect > 5-10 mL of blood in the feces/day (5-10 mg of hemoglobin/ gram of stool) assuming a blood hemoglobin of 15 g/ dL with an average stool passage of 150 g/day.
  
• Peroxidase activity from hemoglobin is diminished with passage through the GI tract, thus bleeding from the upper GI tract is less likely to produce a positive test than bleeding from the lower GI tract. Similarly, hemoglobin is more likely to be digested in the upper GI tract, thus less likely to be detected when a GI bleed originates from the upper GI tract.
  

Interferences

• false positives: (contributions generally NOT significant)

• hemoglobin & myoglobin from meats & fish
• peroxidases from fruits & vegetables
• peroxidases in intestinal flora

• false negatives:

• ascorbate ( vitamin C) > 250 mg QD
• other antioxidants

• iron supplement in the form of ferrous sulfate or gluconate do NOT cause a positive test
• NSAIDs probably don't interfere with iFOBT [4,10]

• aspirin < 1250 mg/day does not interfere
• low-dose aspirin (81 mg QD) compared with no aspirin is associated with a higher sensitivity (71 vs 36%) for detecting advanced colorectal neoplasms, at the cost of a lower specificity (86 vs 91%) [12]

• anticoagulation ( warfarin) does not interfere with iFOBT [10]

Differential-diagnosis

• (of positive test)
• age < 20 years

• Peutz-Jeghers syndrome

• age 20-60 years

• Crohn's disease
• chronic radiation therapy
• NSAID-induced ulcers
• large hiatal hernia, Cameron erosion
• gastric antral vascular ectasia (watermelon stomach)
• malignancy
• von Willebrand disease

• age > 60 years

• amyloidosis
• angiodysplasia (angiectasia)
• hereditary hemorrhagic telangiectasia
• malignancy, especially colorectal cancer

• colorectal cancer

• 50-87% of patients with colorectal cancer yield positive results
• 16-30% reduction in mortality from colon cancer for patients that adhere to annual or biennial testing [2,3]
• 5% cumulative risk of positive fecal occult blood over period of 13 years [2]

Management

• colonoscopy for evaluation of positive fecal occult blood
• insufficient evidence to recommend routine upper endoscopy ( EGD) following negative colonoscopy ( fecal occult blood +) [11]

More General Terms

• clinical hematology test
• point of care test

Additional Terms

• bright red blood per rectum (BRBPR)
• hematochezia
• lower gastrointestinal hemorrhage

References

1. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 539
2. Journal Watch 22(5):38, 2002 Traverso G et al, N Engl J Med 346:311, 2002
3. Journal Watch 24(14):112, 2004 Faivre J, Dancourt V, Lejeune C, Tazi MA, Lamour J, Gerard D, Dassonville F, Bonithon-Kopp C. Reduction in colorectal cancer mortality by fecal occult blood screening in a French controlled study. Gastroenterology. 2004 Jun;126(7):1674-80. PMID: [1]
4. Prescriber's Letter 12(3): 2005 Aspirin and Nonsteroidal Anti-inflammatory Agents and their Effect on Fecal Occult Blood Tests Detail-Document#: [2] (subscription needed) [3]
   - Journal Watch 25(3):29, 2005 Kahi 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. Am J Med. 2004 Dec 1;117(11):837-41. PMID: [4]
5. Prescriber's Letter 12(9): 2005 New Take-Home Screening Tests for Colon Cancer Detail-Document#: [5] (subscription needed) [6]
6. Fraser CG, Matthew CM, Mowat NA, Wilson JA, Carey FA, Steele RJ. Immunochemical testing of individuals positive for guaiac faecal occult blood test in a screening programme for colorectal cancer: an observational study. Lancet Oncol. 2006 Feb;7(2):127-31. PMID: [7]
7. Levi Z, Rozen P, Hazazi R, Vilkin A, Waked A, Maoz E, Birkenfeld S, Leshno M, Niv Y. A quantitative immunochemical fecal occult blood test for colorectal neoplasia. Ann Intern Med. 2007 Feb 20;146(4):244-55. PMID: [8]
   - Imperiale TF. Quantitative immunochemical fecal occult blood tests: is it time to go back to the future? Ann Intern Med. 2007 Feb 20;146(4):309-11. PMID: [9]
8. Guittet L et al, Comparison of a guaiac based and an immunochemical faecal occult blood test in screening for colorectal cancer in a general average risk population Gut 2007, 56:210 PMID: [10]
9. van Rossum LG et al. Random comparison of guaiac and immunochemical fecal occult blood tests for colorectal cancer in a screening population. Gastroenterology 2008 Jul; 135:82. PMID: [11]
10. Levi Z et al Sensitivity, but not specificity, of a quantitative immunochemical fecal occult blood test for neoplasia is slightly increased by the use of low-dose aspirin, NSAIDs, and anticoagulants. Am J Gastroenterol 2009 Apr; 104:933. PMID: [12]
    - Iles-Shih L et al. Prevalence of significant neoplasia in FOBT-positive patients on warfarin compared with those not on warfarin. Am J Gastroenterol 2010 Sep; 105:2030 PMID: [13]
11. Park DI et al. Comparison of guaiac-based and quantitative immunochemical fecal occult blood testing in a population at average risk undergoing colorectal cancer screening. Am J Gastroenterol 2010 Sep; 105:2017 <PubMed> PMID: [14] <Internet> [15]
    - Allison JE. FIT: A valuable but underutilized screening test for colorectal cancer - It's time for a change. Am J Gastroenterol 2010 Sep; 105:2026 <PubMed> PMID: &dopt=Abstract <Internet> [16]
12. Physician's First Watch, Dec 8, 2010 Massachussetts Medical Society [17]
    - Brenner H et al Low-Dose Aspirin Use and Performance of Immunochemical Fecal Occult Blood Tests JAMA. 2010 Dec 8;304(22):2513-20. <PubMed> PMID: [18] <Internet> [19]
13. National Guideline Clearinghouse
    - Gastroscopy following a positive fecal occult blood test and negative colonoscopy: guideline recommendations. Program in Evidence-based Care ngc-guideline: [20]

fecal occult blood; fecal immunochemical testing (FOB, FIT, iFOBT, ColonCARE, Hemoccult, ICT, InSure)