Colorectal Cancer Screening with Guaiac-Based Fecal Occult Blood Test (gFOBT)

Introduction to gFOBT

The American Cancer Society recommends gFOBT as a screening method for colorectal cancer, which detects blood in stool through the pseudoperoxidase activity of heme or hemoglobin 1, 2
The test uses guaiac-impregnated slides that change color when blood is present, with common brand names including Hemoccult II and Hemoccult SENSA 3, 4, 5

The test requires collecting 2 samples from each of 3 consecutive bowel movements at home, which are then applied to guaiac-impregnated cards and developed either in a physician's office or clinical laboratory 1, 2, 3
The guaiac reagent reacts with the peroxidase-like activity of hemoglobin, producing a blue color change if blood is present 2

Three large randomized controlled trials demonstrated that annual gFOBT screening reduces colorectal cancer mortality by 15-33% over 8-13 years, according to the American Cancer Society 1, 2
Only high-sensitivity gFOBT (sensitivity >70% and specificity >90% for cancer) should be used for screening, as recommended by the National Comprehensive Cancer Network 6, 7
The sensitivity of a single gFOBT is low (30-50%), but repeated annual testing can detect up to 92% of cancers, as reported in Gastroenterology 3

Patients must avoid red meat, poultry, fish, and some raw vegetables for 3 days before testing to prevent false positives from dietary pseudoperoxidase activity, as advised by the American Cancer Society 1, 2, 8
NSAIDs and aspirin (>1 adult dose/day) should be avoided for 7 days to reduce false positive results from medication-induced bleeding, according to Praxis Medical Insights 8
Any positive gFOBT must be followed by colonoscopy, not repeat stool testing, as recommended by Gastroenterology and the American Cancer Society 1, 2, 3

High-sensitivity gFOBT (Hemoccult SENSA) has approximately 64.3% sensitivity for colorectal cancer with 3-sample home testing, as reported by Praxis Medical Insights 8
The test must be repeated annually to achieve maximum benefit, as recommended by Gastroenterology, the National Comprehensive Cancer Network, and the American Cancer Society 1, 3, 7
Only high-sensitivity gFOBT that have been shown to detect a majority of prevalent colorectal cancer should be used, according to the American Cancer Society 4, 5
Annual screening is recommended for average-risk adults aged 50 years and older, as advised by Gastroenterology, the National Comprehensive Cancer Network, and the American Cancer Society 1, 3, 7