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

Rationale for Immediate Colonoscopy

A single positive fecal occult blood test (FOBT) in a patient with low hemoglobin requires immediate colonoscopy without repeating the FOBT, as recommended by the American College of Gastroenterology and the National Comprehensive Cancer Network 1, 2, 3
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, according to the National Comprehensive Cancer Network 3, 1
Repeating the FOBT after a positive result is inappropriate and delays proper diagnostic evaluation, as stated by the American Cancer Society and the National Comprehensive Cancer Network 1, 4

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, according to the American College of Gastroenterology 1
Each additional month of delay in diagnostic colonoscopy increases both colorectal cancer incidence and mortality, as reported by the National Comprehensive Cancer Network 1

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, as noted by the American Cancer Society and the National Comprehensive Cancer Network 1, 4
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, according to the American College of Gastroenterology and the National Comprehensive Cancer Network 1, 4
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, as stated by the American College of Gastroenterology 5

For future reference, FOBT should be performed properly with 3 stool samples obtained at home, as recommended by the American Cancer Society and the National Comprehensive Cancer Network 1, 6
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, according to the American College of Gastroenterology and the National Comprehensive Cancer Network 1, 4
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, as noted by the American Cancer Society and the National Comprehensive Cancer Network 1, 6