Differences Between FIT and gFOBT in Colorectal Cancer Screening
FIT is superior to gFOBT for colorectal cancer screening because it detects human globin protein specifically, making it more accurate for lower GI bleeding with higher sensitivity, better specificity, and improved patient compliance due to fewer dietary restrictions and simpler sampling procedures. 1
Key Differences in Detection Mechanism
- FIT detects human globin protein (a component of hemoglobin), making it specific for human blood, while gFOBT detects heme through a peroxidase reaction that can be affected by various factors 2, 1
- Globin is degraded by digestive enzymes in the upper gastrointestinal tract, making FIT more specific for lower gastrointestinal bleeding and improving specificity for colorectal cancer 2, 1
- gFOBT can produce false-positive results due to dietary factors such as rare red meat, cruciferous vegetables, and some fruits that contain peroxidase, while FIT is not affected by these factors 2
- FIT is not subject to false-negative results from high-dose vitamin C supplements, which can block the peroxidase reaction in gFOBT 2, 1
Performance Comparison
- FIT has approximately twice the sensitivity of gFOBT for cancer detection, with studies showing FIT sensitivity of 65-100% compared to gFOBT sensitivity of 30-65% 1, 3
- In direct comparisons, FIT demonstrated superior sensitivity for colorectal cancer (81.8% vs. 64.3% for high-sensitivity gFOBT) 2
- FIT has higher specificity for distal cancer (96.9%), distal advanced lesions (97.3%), and all distal advanced neoplasia (97.5%) compared to high-sensitivity gFOBT 2
- FIT is ineffective at detecting sessile serrated polyps (only 5% sensitivity), which is a limitation to be aware of 2, 1
Patient Experience and Compliance
- FIT requires fewer stool samples (usually 1-2) compared to gFOBT (typically 3), improving patient compliance and comfort 1, 4
- FIT does not require dietary restrictions, making it more convenient for patients 2, 1
- Studies show higher participation rates with FIT (approximately 10-20% higher) compared to gFOBT 1, 5
- Collection kits for FIT have been designed to facilitate specimen collection and mailing, enhancing compliance 2
Clinical Implications
- The American Gastroenterological Association and American College of Gastroenterology recommend FIT over gFOBT for colorectal cancer screening 1, 6
- FIT detects significantly more cancers and advanced adenomas than gFOBT, with one study showing FIT detected 2.5 times more cancers and advanced adenomas than gFOBT despite similar colonoscopy rates 3, 7
- Quantitative FIT allows for adjustment of the hemoglobin concentration cutoff to balance sensitivity and specificity based on available colonoscopy resources 1, 5
- Any positive result from either test requires follow-up colonoscopy, not repeat testing, to ensure accurate diagnosis and treatment 2, 1
Common Pitfalls and Caveats
- In-clinic FOBT performed during digital rectal examination is not recommended for colorectal cancer screening due to extremely poor sensitivity (less than 10%) 2, 1
- Single-sample testing with either method has lower sensitivity than multi-sample testing, though FIT performs better with fewer samples 1, 5
- The optimal number of FIT stool samples is not firmly established, but 2 samples may be superior to one 2
- When selecting between tests, consider factors such as cost (both out-of-pocket and total costs) and likelihood of test completion 2