Do I need multiple positive fecal occult blood tests (FOBT) before proceeding with a colonoscopy in a patient with low hemoglobin (hgb) and anemia?

Management of Positive Fecal Occult Blood Test in a Patient with Low Hemoglobin

A single positive fecal occult blood test (FOBT) in a patient with low hemoglobin requires immediate colonoscopy without repeating the FOBT. 1, 2

Rationale for Immediate Colonoscopy

• Any positive result on FOBT should be followed up with colonoscopy, as this is the definitive diagnostic procedure that 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 2, 1
• Repeating the FOBT after a positive result is inappropriate and delays proper diagnostic evaluation 1, 2
• The combination of low hemoglobin and positive FOBT significantly increases the likelihood of finding colorectal neoplasia, making prompt evaluation essential 3, 4
• Colonoscopy for bleeding indications (including positive FOBT and iron deficiency anemia) has a substantial yield for cancers (approximately 1 per 9 to 13 colonoscopies) 5

Timing of Colonoscopy

• The American Cancer Society recommends that colonoscopy should be performed within 60 days of a positive FOBT result to minimize the risk of disease progression 1
• Delays in follow-up colonoscopy beyond 180 days are associated with increased risk of colorectal cancer in a dose-response fashion 1
• Each additional month of delay in diagnostic colonoscopy increases both colorectal cancer incidence and mortality 1

Common Pitfalls to Avoid

• Do not repeat the FOBT after a positive result - Nearly one-third of physicians inappropriately repeat FOBT after a positive result instead of proceeding directly to colonoscopy 1, 2
• Do not use flexible sigmoidoscopy alone as follow-up - This is inadequate as it only visualizes the distal portion of the colon and may miss significant proximal lesions 1, 2
• Do not attribute a positive FOBT to medications without further evaluation - Physicians should not attribute a positive FOBT to low-dose aspirin or anticoagulant medications without proper evaluation 3
• Do not delay colonoscopy for additional stool testing - In patients with visible blood in stool or anemia plus positive FOBT, delaying colonoscopy for additional stool testing may postpone diagnosis of significant colorectal pathology 6

Additional Considerations for Patients with Anemia

• All patients with iron deficiency anemia and positive FOBT should undergo both colonoscopy and esophagogastroduodenoscopy (EGD) to evaluate for potential bleeding sources throughout the gastrointestinal tract 7, 3
• In patients with anemia and positive FOBT, 91-100% of gastroenterologists recommend both colonoscopy and EGD 7
• If initial colonoscopy and EGD are negative in a patient with recurrent bleeding, repeat procedures may find missed lesions in up to 35% of patients 3
• If no cause is found after EGD and colonoscopy, capsule endoscopy has a diagnostic yield of 61-74% for identifying small bowel sources of bleeding 3

Proper FOBT Testing Technique

• For future reference, FOBT should be performed properly with 3 stool samples obtained at home 1, 2
• A single-stool sample FOBT collected after digital rectal exam in the office has extremely poor sensitivity (only 4.9% for advanced neoplasia) and should not be used for screening 1, 2
• Prior to testing with guaiac-based tests, patients should follow dietary restrictions including avoidance of vitamin C in excess of 250 mg and red meats for 3 days before testing 1, 2