What are the next steps after a positive Fecal Occult Blood Test (FOBT) result?

Next Steps After a Positive Fecal Occult Blood Test (FOBT)

Colonoscopy should be performed within 60 days of a positive FOBT result as the definitive follow-up test to minimize the risk of disease progression. 1

Rationale for Colonoscopy Follow-up

• Colonoscopy is the recommended follow-up test after a positive FOBT as it allows for direct visualization of the entire colon and provides the opportunity to identify and remove adenomatous polyps or detect colorectal cancer at an early stage 1
• Studies show that colonoscopy following positive FOBT detects early colorectal cancer more frequently than advanced cancer, with one study finding 6.4% early cancers versus 4.0% advanced cancers 2
• Delays in follow-up colonoscopy beyond 180 days are associated with increased risk of colorectal cancer in a dose-response fashion, becoming statistically significant after 270 days (OR: 1.48, CI 1.05-2.08) 3
• Each additional month of delay in diagnostic colonoscopy is estimated to increase both CRC incidence and mortality by 0.1 per 1,000 (a 0.3% and 1.4% monthly increase) 3

Timing of Colonoscopy

• Colonoscopy should ideally be performed within 60 days of a positive FOBT result 1
• Empirical evidence shows increased risk for CRC incidence and higher stage disease with wait-times over 180 days 3
• Modeling studies suggest potential increased risk with each additional month of wait time for diagnostic testing 3
• A 12-month delay is estimated to increase CRC incidence by 4% and mortality by 16% 3

Common Pitfalls in FOBT Follow-up

• Inappropriate follow-up practices to avoid:

  • Repeating the FOBT after a positive result is inappropriate and delays proper diagnostic evaluation 1, 4
  • Following up with flexible sigmoidoscopy alone is inadequate as it only visualizes the distal portion of the colon 1
  • Single-sample in-office FOBT collected during digital rectal examination has extremely poor sensitivity (only 4.9% for advanced neoplasia) and should not be used for screening 1, 5

• Barriers to appropriate follow-up:

  • Patient belief that the FOBT+ was a false positive 6
  • Patient fear of colonoscopy 6
  • Competing health issues 6
  • Breakdown in communication of FOBT+ results or colonoscopy appointments 6
  • Recent colonoscopy (within 2 years) is strongly associated with failure to follow up (OR: 4.31) 4

Factors Associated with Higher Rates of Follow-up

• Obtaining the FOBT for routine colorectal screening (OR 1.59) 7
• Consultation with gastroenterology (OR 1.99) 7
• Clear communication with patients about the importance of follow-up colonoscopy 1

Factors Associated with Lower Rates of Follow-up

• Age older than 80 years (OR 0.54) 7
• Age younger than 50 years (OR 0.44) 7
• Being uninsured (OR 0.50) 7
• Having undergone colonoscopy within the prior five years (OR 0.32) 7

Alternative Tests When Colonoscopy Cannot Be Performed

• CT colonography (CTC) can be considered if colonoscopy cannot be performed 3

  • CTC has a per-patient sensitivity of 88.8% for ≥6-mm adenomas or colorectal cancer in FOBT-positive patients 3
  • However, colonoscopy remains the preferred test for FOBT-positive patients when feasible due to the high prevalence of findings requiring intervention 3

• Double-contrast barium enema (DCBE) is less sensitive than CTC but can be used if CTC is not available 3

  • DCBE has sensitivity of 75% to 80% for detecting colorectal cancer in FOBT-positive patients 3

Importance of Proper FOBT Testing

• FOBT must be performed properly with 3 stool samples obtained at home 3
• A single-stool sample FOBT collected after digital rectal exam in the office is not an acceptable screening test 3
• Prior to testing with guaiac-based tests, individuals should avoid NSAIDs and high-dose aspirin for 7 days 3, 5
• Dietary restrictions include avoidance of vitamin C in excess of 250 mg and red meats for 3 days before testing 3, 5

Clinical Implications of Missed Follow-up

• One study found that 62% of patients with advanced colorectal cancer had initially tested FOBT negative, highlighting the importance of proper follow-up and the limitations of FOBT as a standalone test 8
• Approximately one-third of patients with a positive FOBT do not undergo follow-up colonoscopy within 6 months, representing a critical quality gap in colorectal cancer screening programs 4