What is the next step if a fecal occult blood test (FOBT) is positive?

Colonoscopy is the Required Next Step After a Positive FOBT

When a fecal occult blood test is positive, proceed directly to colonoscopy—do not repeat the FOBT, and do not substitute with flexible sigmoidoscopy alone. 1, 2

Why Colonoscopy is Mandatory

• Colonoscopy is the only appropriate follow-up test because it directly visualizes the entire colorectal mucosa and simultaneously allows removal of adenomatous polyps or detection of colorectal cancer at early, treatable stages. 1, 2

• The positive predictive value for significant neoplasia is high when FOBT is positive, making complete colonic evaluation essential rather than optional. 1

• Alternative tests like CT colonography or double-contrast barium enema are inferior options and should only be considered if colonoscopy cannot be performed. 2

Timing is Critical

• Schedule colonoscopy within 60 days of the positive FOBT result to minimize risk of disease progression. 2

• Delays beyond 180 days significantly increase colorectal cancer risk, with statistical significance reached after 270 days (OR: 1.48). 2

• Each additional month of delay increases both colorectal cancer incidence and mortality by approximately 0.1 per 1,000 patients. 2

• A 12-month delay increases cancer incidence by 4% and mortality by 16%. 2

Common Pitfalls to Avoid

Do NOT Repeat the FOBT

• Repeating FOBT after a positive result is inappropriate and delays proper diagnosis—nearly one-third of physicians make this error. 1, 2

• A positive FOBT has already triggered the need for definitive evaluation; repeating it provides no additional useful information. 1, 2

Do NOT Use Flexible Sigmoidoscopy Alone

• Flexible sigmoidoscopy only visualizes the distal colon (less than half the bowel) and will miss significant proximal lesions. 1, 2

• This approach is inadequate as the sole follow-up for positive FOBT. 2

Do NOT Perform Upper Endoscopy Routinely

• In the absence of iron-deficiency anemia or upper gastrointestinal symptoms, a positive FOBT with negative colonoscopy does not warrant upper endoscopy. 1

Special Circumstances

Recent Prior Colonoscopy

• If the patient had a negative colonoscopy within the past 5 years (before being due for repeat screening), generally still offer repeat colonoscopy given FIT's superior performance characteristics compared to guaiac-based FOBT. 1

• Only 1% of guaiac FOBT-positive individuals with negative colonoscopy in the past 5 years had advanced neoplasia, but this still warrants evaluation. 1, 2

• Additional factors supporting repeat colonoscopy include: clinical context (worrisome signs, symptoms, laboratory values), patient risk factors for advanced neoplasia, and quality of prior examination (poor bowel preparation, low adenoma detection rate). 1

If Colonoscopy Cannot Be Performed

• CT colonography has 88.8% per-patient sensitivity for ≥6-mm adenomas or colorectal cancer in FOBT-positive patients and is the preferred alternative. 2

• Double-contrast barium enema is less sensitive (75-80% for colorectal cancer) but can be used if CT colonography is unavailable. 2

Important Context: Proper FOBT Collection

While not directly relevant to managing a positive result, understanding proper collection helps contextualize the test's validity:

• Valid FOBT requires 3 stool samples from consecutive bowel movements collected at home, not a single office sample during digital rectal examination. 1, 2, 3

• Single-sample office FOBT has unacceptably poor sensitivity of only 4.9% for advanced disease and should never be used for screening. 2, 3