What is the reliability of the Fecal Immunochemical Test (FIT) for bowel cancer screening?

From the Guidelines

The Fecal Immunochemical Test (FIT) is a reliable screening tool for bowel cancer, with a pooled sensitivity of 79% (95% CI, 0.69-0.86) for CRC and a specificity of 94% (95% CI, 0.92-0.95), as reported in a meta-analysis of 19 studies in asymptomatic average-risk adults 1.

Key Points

• The sensitivity of FIT can be adjusted by altering the threshold for a positive result, but this may impact specificity negatively 1.
• A very large and recent US study found that the FDA-cleared OC FIT CHEK had a sensitivity and specificity for cancer of 74% and 96%, respectively 1.
• FIT is more specific than older guaiac-based tests because it only detects human hemoglobin, reducing false positives from dietary sources.
• The test is typically performed every 2 years, requiring a single stool sample that patients can collect at home, as recommended by the American College of Physicians 1.

Screening Recommendations

• For average-risk individuals, FIT screening typically begins at age 45-50 and continues until age 75, though specific recommendations may vary based on individual risk factors and family history.
• Clinicians should select the colorectal cancer screening test with the patient on the basis of a discussion of benefits, harms, costs, availability, frequency, and patient preferences 1.
• Suggested screening tests and intervals are FIT or high-sensitivity guaiac-based fecal occult blood testing every 2 years, colonoscopy every 10 years, or flexible sigmoidoscopy every 10 years plus FIT every 2 years 1.

Important Considerations

• Any positive FIT result requires follow-up with a colonoscopy for definitive diagnosis.
• No screening test is perfect - a negative result doesn't guarantee absence of cancer, and a positive result doesn't necessarily mean cancer is present.
• Patient informed decision making and adherence are important factors in selection of a CRC screening test, and discussion should include topics such as suggested frequency, bowel preparation, anesthesia, transportation, and time commitments 1.

From the Research

Reliability of Fecal Immunochemical Test (FIT) for Bowel Cancer Screening

The reliability of the Fecal Immunochemical Test (FIT) for bowel cancer screening can be evaluated based on its diagnostic accuracy, sensitivity, and specificity.

• The average sensitivity of FIT for colorectal cancer (CRC) was 93% (95% CI, 53%-99%), and the average specificity was 91% (95% CI, 89%-92%) 2.
• A study found that repeating FIT provides greater differentiation of patients with and without CRC, but is associated with decreased specificity and positive predictive value 3.
• The summary sensitivity of FIT for CRC detection was 88.7% (95% CI, 85.2 to 91.4) and the specificity was 80.5% (95% CI, 75.3 to 84.8) at the most commonly reported f-Hb positivity threshold of ≥ 10 µg Hb/g faeces 4.
• FIT sensitivity may be higher in patients reporting rectal bleeding, and single quantitative FIT at lower f-Hb positivity thresholds can adequately exclude colorectal cancer in symptomatic patients 4.
• The sensitivity of FIT for CRC detection differs according to stage and location, with lower sensitivity for early-stage cancers and those located in the distal colon 5.

Factors Affecting FIT Reliability

Several factors can affect the reliability of FIT for bowel cancer screening, including:

• FIT cutoff values: Subgroup analyses indicated that FIT cutoff values between 15- and 25-μg/g feces provided the best combination of sensitivity and specificity for the diagnosis of CRC 2.
• Risk factors: Risk scoring systems that combine the FIT concentration with risk factor assessment have been shown to improve the sensitivity of the test 6.
• Tumor location and stage: The sensitivity of FIT for CRC detection varies according to tumor location and stage, with lower sensitivity for early-stage cancers and those located in the distal colon 5.

Implications for Clinical Practice

The reliability of FIT for bowel cancer screening has implications for clinical practice, including:

• FIT can be used as a triaging tool for patients with symptoms of possible colorectal cancer, with single quantitative FIT at lower f-Hb positivity thresholds providing a data-based approach to prioritization of colonoscopy resources 4.
• Repeating FIT may provide greater differentiation of patients with and without CRC, but its application may be restricted due to the associated increase in investigations 3.
• Risk-based colorectal cancer screening using FIT may enable those at greatest risk to be referred for colonoscopy, optimizing resource use and ultimately patient outcomes 6.