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Fecal Occult Blood Test (FOBT): Optimal Testing Recommendations
There are two main FOBT technologies: guaiac or gFOBT and fecal immunochemical tests or FIT. Outpatient gFOBT testing is not recommended. The FIT should be used instead, specifically for colorectal cancer screening.
Guidelines for Test Utilization
- What does the test tell me?
- When should I order this test?
- When should I NOT order this test?
- How should I interpret the result?
- Is the test result diagnostic/confirmatory of the condition? If not, is there a diagnostic/confirmatory test?
- Are there factors that can affect the lab result?
- Are there considerations for special populations?
- What other test(s) might be indicated?
What does the test tell me?
It detects the presence of heme minute quantities of (blood) in the stool through a chemical reaction. It was historically used to screen for occult malignancy or lower gastrointestinal (GI) bleeding. While FOBT testutlize chemical reaction to pick up HEME fecal immuno test is more specific as it uses antibody test to use globin. [back to top]
When should I order this test?
Rarely to never. While gFOBT previously used for iron deficiency anemia (IDA) or ulcerative colitis, it lacks the necessary clinical utility for these conditions. No dietary restrictions are required for this test. [back to top]
When should I NOT order this test?
Do not order for routine colorectal cancer screening (use FIT instead) or for adult inpatients. It should not be used as a primary tool for diagnosing positive stool cultures. [back to top]
How should I interpret the result?
A positive result indicates potential GI bleeding but lacks specificity. Sensitivity for iron deficiency anemia is only 58%, and for positive stool cultures, it is as low as 38%. [back to top]
Is the test result diagnostic/confirmatory of the condition? If not, is there a diagnostic/confirmatory test?
No, it is a screening tool with poor sensitivity/specificity. A positive result requires diagnostic follow-up, typically via a colonoscopy or endoscopy. [back to top]
Are there factors that can affect the lab result?
FOBT is prone to false positives from diet (e.g., red meat, certain vegetables) and medications (e.g., NSAIDs, Vitamin C), unlike the more specific FIT. [back to top]
Are there considerations for special populations?
In adult populations, the test has been largely phased out due to its limited diagnostic value compared to newer alternatives. [back to top]
What other test(s) might be indicated?
Fecal Immunochemical Test (FIT) for colorectal cancer screening. Direct referral for endoscopic evaluation is recommended for suspected occult GI bleeds. [back to top]
References
Lee MW, Pourmorady JS, Laine L. Use of Fecal Occult Blood Testing as a Diagnostic Tool for Clinical Indications: A Systematic Review and Meta-Analysis. Am J Gastroenterol. 2020 May;115(5):662-670. doi: 10.14309/ajg.0000000000000495.
Last reviewed: August 2025. The content for Optimal Testing: the Association for Diagnostics & Laboratory Medicine’s (ADLM) Guide to Lab Test Utilization has been developed and approved by the Academy of Diagnostics & Laboratory Medicine and ADLM’s Science and Practice Core Committee.
As the fields of laboratory medicine and diagnostic testing continue to grow at an incredible rate, the knowledge and expertise of clinical laboratory professionals is essential to ensure that patients receive the highest quality and most useful laboratory tests. ADLM’s Academy and Science and Practice Core Committee have developed a test utilization resource focusing on commonly misused tests in hospitals and clinics. Improper test utilization can result in poor patient outcomes and waste in the healthcare system. This important resource geared toward medical professionals recommends better tests and diagnostic practices. Always consult your laboratory director to make sure these recommendations are appropriate for your patient population.