Gastroenterology Book

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Fecal Occult BloodAka: Stool Guaiac, Stool Occult Blood, FOBT, Hemoccult, Heme-Porphyrin Test, Hemoquant, Immunochemical Fecal Occult Blood, HemeSelect, FECA-EIA

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  1. See Also
    1. Gastrointestinal Bleeding
    2. Gastrointestinal Occult Bleeding Causes
  2. Available Tests
    1. Guaiac-Based Test (Hemoccult)
      1. Reagent derived from wood resin of Guajacum trees
      2. Reaction based on presence of Hemoglobin in sample
        1. Hemoglobin contains pseudoperoxidase
        2. Pseudoperoxidase converts guaiac to blue
        3. Reaction requires addition of hydrogen peroxide
    2. Heme-Porphyrin Test (Hemoquant)
      1. Quantifies porphyrins from Hemoglobin
      2. Advantages
        1. Measures amount of stool blood present
        2. Food-based peroxidases do not give false positives
      3. Disadvantages
        1. Expensive and requires increased lab staff time
        2. High false positive rate
    3. Immunochemical Fecal Occult Blood: HemeSelect, FECA-EIA
      1. Identifies only intact human Hemoglobin
      2. Advantages
        1. Ingested red meat does not give false positive
        2. Food-based peroxidases do not give false positives
        3. Specific for lower gastrointestinal tract bleeding
      3. Disadvantages
        1. Requires increased lab staff time
        2. Detects only lower gastrointestinal tract bleeding
  3. Efficacy in Colon Cancer Screening (Guaiac tests)
    1. USPSTF Strength of Recommendation: B
    2. Screening picks up 26% of Colorectal Cancer
    3. Lowers Colon Cancer mortality (versus no screening)
      1. Annual screening: 33% reduction
      2. Biennial (every 2 years): 15-21% reduction
    4. References
      1. Kronberg (1996) Lancet 348:1467
      2. Hardcastle (1996) Lancet 348:1472
      3. Mandel (2000) N Engl J Med 343:1603
      4. Mandel (1999) J Natl Cancer Inst 91:434
  4. Indications
    1. Start Occult blood screening by age 50 years old
  5. Technique
    1. Use guaiac-based tests (Hemoccult)
    2. Minimize False Positive Rate
      1. See False positives below
      2. Avoid listed items for 3 days prior to testing
      3. Aspirin and NSAIDs appear to be safe prior to FOBT
        1. (2005) Prescriber's Letter p. 15
    3. Minimize False Negative Rate
      1. Avoid Vitamin C >250 mg/day for 2 days before test
      2. Test 2 samples from each of 3 consecutive stools
      3. Space samples over 4-6 days
    4. Digital Rectal Exam does not increase false positives
      1. Bini (1999) Arch Intern Med 159:2022
  6. Causes of false positive Guaiac tests (Hemoccult)
    1. Foods associated with false positive FOBT
      1. Common Causes
        1. Red meat
        2. Cantaloupe and other melon
        3. Grapefruit
        4. Figs
        5. Broccoli
        6. Turnips
        7. Radishes
        8. Horseradish
        9. Cauliflower
      2. Uncommon causes of false positive FOBT
        1. Cucumber
        2. Carrot
        3. Cabbage
        4. Potato
        5. Pumpkin
        6. Zucchini
        7. Parsley
    2. Medications and Supplements
      1. Previously ASA NSAIDS thought to cause false positive
        1. Now both are thought to be safe prior to FOBT
        2. Avoid doses of ASA >1250 mg/day
      2. Medications that do not result in false positives
        1. Coumadin
    3. Miscellaneous causes of false positive FOBT
      1. Nasal bleeding source (e.g. Epistaxis)
      2. Oral bleeding source
        1. Gingival bleeding
        2. Tonsillitis
      3. Pulmonary bleeding source (e.g. Hemoptysis)
      4. Long distance Running
  7. Causes of positive occult blood test
    1. Gastrointestinal Occult Bleeding Causes
  8. References
    1. Rockey in Feldman (2002) Sleisenger GI, p. 232-48
    2. Herold in Rakel (2002) Family Practice, p. 1563-4

Fecal occult blood test (C0201811)

Definition (NCI)(FEE-kul o-KULT) A test to check for blood in stool. (Fecal refers to stool; occult means hidden.)
Definition (NCI)A noninvasive test that detects the presence of hidden (occult) blood in the stool. This is commonly performed to screen for colon cancer.
ConceptsLaboratory Procedure (T059)
EnglishChemical test for occult blood, Faecal occult blood, Faecal occult blood screen, Faecal occult blood screening, Faecal occult blood test, Faeces occult blood, Fecal occult blood screen, Fecal occult blood screening, Fecal occult blood test, Feces occult blood, FOBT, Guaiac Smear Test, Guaiac test, Hemoccult, Screening for occult blood in faeces, Screening for occult blood in feces, Stool guaiac test
Spanishcribado de sangre oculta en las heces, detección selectiva de sangre oculta en las heces, detección selectiva de sangre oculta en los excrementos, deteccion selectiva de sangre oculta en las heces, deteccion selectiva de sangre oculta en los excrementos, prueba de Almén para sangre, prueba de Almen para sangre, prueba de sangre oculta en materia fecal, prueba del guayaco, prueba química para detección de sangre oculta, prueba quimica para deteccion de sangre oculta, tamizaje de sangre oculta en las heces
CreditsDerived from the NIH UMLS (Unified Medical Language System)



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