Fecal Occult Blood

Aka: Fecal Occult Blood, Fecal Occult Blood Test, Stool Guaiac, Stool Occult Blood, FOBT, Hemoccult, Heme-Porphyrin Test, Hemoquant, Immunochemical Fecal Occult Blood, HemeSelect, FECA-EIA, Fecal Immunochemical Test, FIT-DNA, ColoGuard, Multitarget Stool DNA Test

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II. Indications

  1. Acute Gastrointestinal Bleeding
  2. Colon Cancer screening
    1. Start Occult blood screening by age 50 years old (or per Colorectal Cancer Screening protocol)

III. Preparations

  1. Guaiac-Based Test (gFOBT, 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
    3. Most commonly used test (for both GI Bleeding, Colorectal Cancer Screening)
      1. Do not use office based testing for screening
    4. Efficacy for gFOBT in Colorectal Cancer Screening (based on 3 home samples submitted)
      1. Test Sensitivity: 62-79%
      2. Test Specificity: 87-96%
      3. Positive Likelihood Ratio: 4.7 to 19.8
      4. Negative Likelihood Ratio: 0.2 to 0.4
      5. Holme (2013) Cochrane Database Syst Rev (9):CD009259 [PubMed]
  2. Fecal Immunochemical Test (FIT, HemeSelect, FECA-EIA, OC-Micro, OC-Sensor, OC-Light)
    1. Identifies only intact human Hemoglobin
    2. Efficacy in screening for Colorectal Cancer
      1. Test Sensitivity: 73-89%
      2. Test Specificity: 92-95%
      3. Lee (2014) Ann Intern Med 160(3): 171-81 [PubMed]
    3. 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
    4. Disadvantages
      1. Requires increased lab staff time
      2. Detects only lower Gastrointestinal Tract bleeding
  3. Fecal Immunochemical with DNA Test or Multitarget Stool DNA Test (FIT-DNA, ColoGuard)
    1. Combination of FIT testing (see above) and DNA biomarkers
      1. Detects Hemoglobin (as does FIT)
      2. Detects Colorectal Cancer and precancer related DNA mutations and methylations
    2. Much more expensive than FIT Testing alone ($680 vs $70)
    3. Efficacy in screening for Colorectal Cancer
      1. Test Sensitivity: 92%
        1. Far more sensitive than FIT Testing (74% sensitive)
      2. Test Specificity: 87 to 90%
        1. Less specific (more False Positives) than FIT Testing (95% specific)
    4. References
      1. Imperiale (2014) N Engl J Med 370(14): 1287-97 [PubMed]
      2. Olson (2020) BMJ Open Gastroenterol 7(1): e000353 [PubMed]
  4. 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

IV. Efficacy: 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 348:1467-71 [PubMed]
    2. Hardcastle (1996) Lancet 348:1472-7 [PubMed]
    3. Mandel (2000) N Engl J Med 343:1603-7 [PubMed]
    4. Mandel (1999) J Natl Cancer Inst 91:434-7 [PubMed]

V. Technique: Guaiac tests (Hemoccult)

  1. Use high-sensitivity guaiac-based tests (Hemoccult Sensa)
  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 [PubMed]

VI. Causes: 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

VII. Causes: Positive occult blood test

  1. Gastrointestinal Occult Bleeding Causes

VIII. References

  1. Rockey in Feldman (2002) Sleisenger GI, p. 232-48
  2. Herold in Rakel (2002) Family Practice, p. 1563-4
  3. Wilkins (2018) Am Fam Physician 97(10): 658-65 [PubMed]

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Related Studies

Ontology: Fecal occult blood test (C0201811)

Definition (NCI_NCI-GLOSS) A test to check for blood in the stool. Small samples of stool are placed on special cards and sent to a doctor or laboratory for testing. Blood in the stool may be a sign of colorectal cancer.
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.
Concepts Laboratory Procedure (T059)
SnomedCT 123215002, 80556006, 270024004, 167665003, 167670005, 144890002, 144895007, 104435004
LNC LA15406-4
English FOB - Faecal occult blood screen, FOB - Fecal occult blood screen, FOB-Faecal occult blood screen, FOB-Fecal occult blood screen, Faecal occult blood test, FOBT - Faec occult blood test, FOBT - Faecal occult blood test, FOBT - Fecal occult blood test, Guaiac test, NOS, fecal occult blood, fecal occult blood (lab test), occult blood test - stool, stool test, test stool, guaiac stool test, blood occult stool test, stool occult blood test, blood fecal occult, guaiac stool tests, guaiac testing, blood fecal occult tests, blood fecal occult testing, fecal occult blood screening, stools test, fecal blood occult, occult fecal blood, stool guaiac test, guaiac test, stool tests, occult blood fecal, faecal occult blood test, stool blood occult test, stool testing, stools testing, faecal occult blood, guaiac tests, Blood, occult - feces, Faecal occult blood NOS, Fecal occult blood &/or test, Faecal occult blood &/or test (procedure), Occult blood - feces, Guaiac test, Fecal occult blood NOS (procedure), Faecal occult blood NOS (procedure), Faecal occult blood &/or test, Blood, occult - faeces, Fecal occult blood NOS, Occult blood - faeces, Feces occult blood, Fecal occult blood test (procedure), Guaiac test (procedure), Faeces occult blood, FOBT, Stool occult blood, Stool Occult Blood Test, Screening for occult blood in feces, Faecal occult blood screen, Fecal occult blood screen, Screening for occult blood in faeces, Chemical test for occult blood (procedure), Chemical test for occult blood, FOB - Faecal occult blood screening, FOB - Fecal occult blood screening, Faecal occult blood screening, Fecal occult blood screening, Screening for occult blood in feces (procedure), fecal occult blood test, Chemical test for occult blood, NOS, Guaiac test -RETIRED-, Fecal Occult Blood Test, Guaiac Smear Test, Hemoccult, Stool guaiac test, Fecal occult blood test, Faecal occult blood, Fecal occult blood, Stool Guaiac test
Dutch fecaal occult bloed, ontlasting guajac test
French Sang occulte fécal, Sang occulte dans les selles, Test des selles au Guaïac
German okkultes Blut im Stuhl, Guajakprobe im Stuhl
Italian Analisi delle feci con guaiaco, Sangue occulto nelle feci
Portuguese Sangue oculto nas fezes, Teste de Guaiac às fezes
Spanish Sangre oculta en heces, Prueba de guayacol en heces, cribado mediante detección de sangre oculta en heces, cribado mediante detección de sangre oculta en materia fecal, detección selectiva de sangre oculta en los excrementos, cribado de sangre oculta en las heces, rastreo mediante detección de sangre oculta en materia fecal, tamizaje de sangre oculta en las heces, detección selectiva de sangre oculta en las heces (procedimiento), detección selectiva mediante la determinación de sangre oculta en materia fecal, cribaje mediante detección de sangre oculta en materia fecal, pesquisa mediante detección de sangre oculta en materia fecal, cribado mediante detección de sangre oculta en materia fecal (procedimiento), tamizaje mediante detección de sangre oculta en materia fecal, detección selectiva de sangre oculta en las heces, screening mediante detección de sangre oculta en materia fecal, prueba del guayaco, determinación de sangre oculta en materia fecal, SAI, test del guayaco - RETIRADO - (concepto no activo), prueba de Almén para sangre, determinación de sangre oculta en materia fecal, SAI (procedimiento), test del guayaco - RETIRADO -, Fecal occult blood NOS, prueba de sangre oculta en materia fecal, prueba de sangre oculta en materia fecal (procedimiento), Faecal occult blood NOS, prueba química para detección de sangre oculta (procedimiento), prueba química para detección de sangre oculta
Japanese 便グアヤック試験, 便潜血, ﾍﾞﾝｾﾝｹﾂ, ﾍﾞﾝｸﾞｱﾔｯｸｼｹﾝ
Czech Okultní krvácení do stolice, Test okultního krvácení do stolice
Hungarian Széklet occult vér, Széklet guaiacol vizsgálat
Derived from the NIH UMLS (Unified Medical Language System)

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