How to ensure reliability of Fecal Immunochemical Test (FIT) for colorectal cancer screening?

Ensuring Reliability of Fecal Immunochemical Test (FIT) for Colorectal Cancer Screening

To ensure reliable FIT results for colorectal cancer screening, use quantitative FIT tests with automated reading and a low hemoglobin threshold (≤20 μg/g), collect a single spontaneously passed stool sample annually, and implement quality assurance practices throughout the screening program. 1

Optimal FIT Selection and Implementation

Test Type Selection

• Choose quantitative FITs over qualitative FITs due to:
  • Better quality control with automated reading
  • Ability to adjust hemoglobin cut-off values
  • More consistent performance characteristics
  • Reduced subjectivity in interpretation 1

Hemoglobin Threshold

• Use a lower threshold cut-off (≤20 μg/g) to define a positive test
• Lower thresholds provide better sensitivity for colorectal cancer detection while maintaining acceptable specificity
• At cut-off values <20 μg/g, sensitivity for CRC is approximately 86% compared to 67% at cut-offs >50 μg/g 1

Sample Collection Protocol

• Use a one-sample annual FIT approach rather than multi-sample testing
  • Single-sample testing shows similar sensitivity (79%) compared to 2-sample (77%) or 3-sample (80%) protocols
  • Simpler collection improves patient adherence 1
• Collect spontaneously passed stool specimens rather than in-office digital rectal examination samples
• Instruct patients that they do not need to adjust diet or medications before completing FIT 1

Quality Assurance Practices

Implement a comprehensive quality assurance program with these target metrics:

• FIT completion rate of at least 60% among those offered testing
• Less than 5% of returned FITs that cannot be processed by the laboratory
• Colonoscopy completion rate of at least 80% for those with positive FIT
• Adenoma detection rate >45% in men and >35% in women during follow-up colonoscopies 1

Handling Positive Results

• When FIT is positive, colonoscopy is the recommended follow-up test 1
• The sensitivity of FIT for detecting colorectal cancer ranges from 74-100%, with specificity of 87-97% 1, 2
• Be aware that FIT sensitivity varies by cancer stage and location:
  • Lower sensitivity for early-stage cancers (68% for stage I vs. 89-92% for stages II-IV)
  • Particularly limited sensitivity (32%) for T1 cancers in the distal colon 3

Common Pitfalls and Solutions

Temperature Considerations

• Programs using FIT need not adjust distribution or mailing based on ambient temperature 1

Test Performance Variability

• Performance characteristics vary widely across FIT manufacturers
• Some qualitative FITs have shown quality control issues, with inconsistent positive results at preset cut-off values 1
• InSure FIT has demonstrated higher sensitivity (26.3%) for advanced colorectal neoplasia compared to OC FIT-CHEK (15.1%) and Hemoccult II SENSA (7.4%) 4

Follow-up Considerations

• In the absence of signs/symptoms of upper GI pathology, a positive FIT with negative colonoscopy should not prompt upper GI evaluation 1
• For patients with a positive FIT who had a recent colonoscopy, repeat colonoscopy is generally recommended 1

Monitoring Program Effectiveness

Track key performance indicators to ensure program quality:

• Positivity rates (expected range: 5-14% for thresholds <20 μg/g)
• Advanced neoplasia detection rates (expect approximately 20% increase in cancer detection)
• Colonoscopy follow-up completion rates
• Interval cancer rates 1

By implementing these evidence-based practices, healthcare providers can maximize the reliability and effectiveness of FIT for colorectal cancer screening.