Guaiac Occult Blood, Fecal, Non Neoplasm Screen (FOBT, LAB4962)

Fecal Occult Blood Testing (FOBT) should not be used in hospitalized patients to evaluate for gastrointestinal bleeding.

Clinical Background
  • Fecal Occult Blood Testing (FOBT) is a non-invasive diagnostic method used to detect hidden (occult) blood in the stool, which is not visible to the naked eye. The primary use of FOBT is for colorectal cancer screening in outpatient settings, particularly recommended for asymptomatic adults as part of routine cancer detection protocols. The presence of occult blood can be an early sign of colorectal cancer or other conditions, such as polyps, ulcers, or inflammatory bowel disease.
  • Despite its utility in screening, FOBT is often misapplied in hospital settings where it is used to evaluate hospitalized patients for gastrointestinal bleeding. This practice is controversial due to:
    • Sensitivity and Specificity Concerns: FOBT has a significant rate of false negatives (30-50%) and false positives (12-30%), which can lead to misdiagnosis or delay in appropriate treatment. False positives may occur due to the test’s reaction to certain foods or medications, and false negatives can result from intermittent bleeding.
    • Clinical Implications in Inpatient Settings: Inappropriate use of FOBT in inpatients often leads to unnecessary follow-up procedures, delayed consultations with specialists, and/or potential mismanagement of actual gastrointestinal conditions.
  • Research and academic consensus, as evidenced by practice changes at several institutions, suggest that the inpatient use of stool guaiac testing, a form of FOBT, should be discontinued due to these limitations and potential harms.
  • As an alternative, more direct and appropriate diagnostic approaches, such as endoscopy, are recommended for hospitalized patients presenting symptoms indicative of gastrointestinal bleeding. These methods offer direct visualization and more accurate diagnosis, significantly impacting patient management and outcomes more effectively than FOBT.
Common Pitfalls
  • High false negative and false positive rates obfuscate the correct treatment plan for inpatients in which occult GI bleed is being considered.
  • Delays in appropriate diagnostic and therapeutic procedures may result from falsely negative results, while falsely positive results contributing to unnecessary downstream testing.
Key Takeaways
  • Fecal occult blood testing is FDA-approved as a screening tool for colorectal cancer in asymptomatic outpatients.
  • Fecal occult blood testing should not play a role in the diagnosis of upper GI bleeding, nor in the assessment of iron-deficiency anemia.
  • Clinical history and physical examination are more reliable tools for managing occult bleeding.
References
  1. Ko, Cynthia W., et al. “AGA Clinical Practice Guidelines on the Gastrointestinal Evaluation of Iron Deficiency Anemia.” Gastroenterology, vol. 159, no. 3, 2020, pp. 1085-1094.
  2. Chiang, Tsung-Hsien., et al. “Performance of the immunochemical fecal occult blood test in predicting lesions in the lower gastrointestinal tract”. CMAJ, vol. 183, no. 3, 2011, pp. 1474-1481.
  3. https://www.accessdata.fda.gov/cdrh_docs/pdf/K972763.pdf. Accessed on July 6, 2024 1:13 PM

Written by: Nicholas Spies, MD

Reviewed by: Ann Gronowski, PhD

Last Edited: 2024-08-29

Last Reviewed: 2024-08-29