Management of Positive FOBT
Proceed directly to colonoscopy within 60 days after a positive FOBT result—do not repeat the FOBT. 1
Definitive Follow-Up Test
Colonoscopy is the only recommended follow-up test for a positive FOBT in screen-eligible individuals. 2 This recommendation is based on colonoscopy's ability to directly visualize the entire colorectal mucosa while simultaneously removing significant neoplasia. 2 The positive predictive value for significant neoplasia is high when FOBT is positive, making colonoscopy the optimal diagnostic and therapeutic approach. 2
Critical Timing
- Complete colonoscopy within 60 days of the positive result to minimize risk of disease progression. 1
- Delays beyond 180 days significantly increase colorectal cancer risk in a dose-response fashion, becoming statistically significant after 270 days (OR: 1.48,95% CI 1.05-2.08). 1
- Each additional month of delay increases both CRC incidence and mortality by 0.1 per 1,000 (representing a 0.3% and 1.4% monthly increase respectively). 1
- A 12-month delay increases CRC incidence by 4% and mortality by 16%. 1
Common Pitfalls to Avoid
Do not repeat the FOBT after a positive result. 1, 3 Nearly one-third of physicians inappropriately repeat FOBT instead of proceeding directly to colonoscopy, which delays proper diagnostic evaluation. 1 This practice is explicitly discouraged by major gastroenterology societies. 2, 3
Do not use flexible sigmoidoscopy alone as follow-up. 1, 3 Sigmoidoscopy only visualizes the distal colon and may miss significant proximal lesions, making it inadequate for evaluating a positive FOBT. 1
Do not perform upper endoscopy routinely. 2 In the absence of iron-deficiency anemia or signs/symptoms of upper gastrointestinal pathology, a positive FOBT with negative colonoscopy should not prompt upper GI evaluation. 2 Research shows that colonoscopy should be the initial procedure of choice, as same-day dual endoscopy is not cost-effective. 4
Special Circumstances
Recent Prior Colonoscopy
If the patient had a recent colonoscopy (within 5 years before being due for repeat examination), generally still offer repeat colonoscopy given FIT's superior performance characteristics compared to guaiac-based FOBT. 2 Additional considerations include:
- Clinical context (other worrisome signs, symptoms, or laboratory values) 2
- Patient risk factors for advanced neoplasia 2
- Prior colonoscopy quality (bowel preparation adequacy, endoscopist's adenoma detection rate) 2
- Note that only 1% of guaiac FOBT-positive individuals with negative colonoscopy within the past 5 years were found to have advanced neoplasia 2
If Colonoscopy Cannot Be Performed
- CT colonography (CTC) can be considered as an alternative, with per-patient sensitivity of 88.8% for ≥6-mm adenomas or colorectal cancer in FOBT-positive patients. 1
- Double-contrast barium enema (DCBE) is less sensitive (75-80% for detecting CRC) but can be used if CTC is unavailable. 1
Expected Findings
When colonoscopy is performed after positive FOBT, approximately: