What is the preferred test between Fecal Occult Blood Test (FOBT) and Fecal Immunochemical Test (FIT) for colorectal cancer screening?

FIT is Superior to FOBT for Colorectal Cancer Screening

Fecal Immunochemical Test (FIT) is strongly recommended over guaiac-based Fecal Occult Blood Test (gFOBT) for colorectal cancer screening due to its superior sensitivity, comparable specificity, and higher patient adherence rates. 1

Diagnostic Performance Comparison

Sensitivity and Specificity

• FIT demonstrates significantly higher sensitivity for colorectal cancer detection (73-88%) compared to gFOBT (30-65%), essentially doubling the cancer detection capability while maintaining similar specificity. 2, 3
• Multiple studies show FIT's superior cancer detection sensitivity: 84.6% for FIT vs. 30.8% for gFOBT (Park et al.), and 100% for FIT vs. 54.2% for gFOBT (Parra-Blanco et al.). 1
• When threshold levels are adjusted to achieve similar positivity rates, FIT sensitivity for colorectal cancer remains twice as high as gFOBT (73.3% vs. 33.3%) with comparable specificity (>95%). 1
• For advanced neoplasia detection, FIT significantly outperforms gFOBT with a relative risk of 2.28 (95% CI, 1.68-3.10). 1

Technical Advantages

• FIT specifically detects human hemoglobin in stool, while gFOBT only detects heme, making FIT more specific for lower GI bleeding. 3, 4
• Unlike gFOBT, FIT is not affected by:
  • Upper GI bleeding (globin is degraded by digestive enzymes) 3
  • Vitamin C supplements (which can cause false-negative gFOBT results) 3
  • Diet or medications (no dietary restrictions required) 1

Patient Experience and Adherence

• FIT requires fewer stool samples (typically 1-2) compared to gFOBT (3 samples), significantly improving patient compliance. 1, 3
• Multiple randomized controlled trials show approximately 10-20% higher participation rates with FIT compared to gFOBT. 1
• Specific participation rate comparisons include:
  • 59.6% for FIT vs. 46.9% for gFOBT (Van Rossum et al.) 1
  • 61.5% for FIT vs. 49.5% for gFOBT (Hol et al.) 1
  • 35.8% for FIT vs. 30.4% for gFOBT (Federici et al.) 1

Advanced Features of FIT

• Quantitative FITs allow for adjustment of hemoglobin concentration cutoff values to balance sensitivity and specificity based on available colonoscopy resources. 2, 3
• Lower cutoff values increase sensitivity for advanced adenomas but decrease specificity: decreasing from 20 to 10 μg/g increases sensitivity from 29% to 35%, with specificity decreasing from 97% to 93%. 2
• FIT has been incorporated into more advanced screening tests like multitarget stool DNA testing, which further improves sensitivity for cancer (92.3% vs. 73.8%) and advanced lesions (42.4% vs. 23.8%), though with lower specificity (86.6% vs. 94.9%). 1

Important Limitations and Caveats

• FIT has poor sensitivity (approximately 5%) for sessile serrated polyps, which are important precursors to colorectal cancer. 1, 3
• Any positive result from either test requires follow-up colonoscopy, not repeat testing, due to the high positive predictive value for cancer detection. 1
• Single-sample testing has lower sensitivity than multi-sample testing, highlighting the importance of proper test protocol. 3
• In-clinic FOBT performed during digital rectal examination is not recommended for colorectal cancer screening due to extremely poor sensitivity (<10%). 3

Implementation Considerations

• Programs implementing FIT should establish systems to track testing cycles and ensure appropriate follow-up of positive results. 1
• The superior performance characteristics of FIT make it the preferred non-invasive screening method for colorectal cancer, despite the availability of newer molecular biomarker tests that may have higher sensitivity but lower specificity and higher costs. 5
• Multiple rounds of FIT testing (annual or biennial) are recommended to maximize the effectiveness of cancer detection and prevention. 1, 2