FIT Testing Should Be Repeated Every 2 Years for Colorectal Cancer Screening
For average-risk adults undergoing colorectal cancer screening with fecal immunochemical testing (FIT), the test should be repeated every 2 years (biennially). This recommendation is based on the strongest guideline evidence and provides the optimal balance between cancer detection and screening burden.
Guideline-Based Recommendation
The American College of Physicians (ACP) 2019 guidance statement explicitly recommends fecal immunochemical testing every 2 years as one of the suggested screening intervals for average-risk adults aged 50-75 years 1. This biennial interval is also supported by:
- Canadian Task Force on Preventive Health Care (CTFPHC): Strong recommendation for FOBT (either gFOBT or FIT) every 2 years for adults aged 50-74 years 1
- U.S. Multi-Society Task Force on Colorectal Cancer (MSTF): Recommends annual FIT as a tier 1 option, though biennial testing remains acceptable 1
Why Every 2 Years?
The biennial interval is based on several key considerations:
Evidence from randomized controlled trials: Most RCT data examining stool-based screening used biennial testing intervals, providing the strongest evidence base for this frequency 1. The CTFPHC specifically chose the 2-year interval because the trial evidence supporting mortality reduction came from studies using this schedule.
Balance of benefits and burdens: A 2-year interval provides:
- Adequate time for detectable lesions to develop
- Reduced false-positive rates compared to annual testing
- Lower colonoscopy burden from follow-up procedures
- Improved patient adherence compared to annual testing
Mortality reduction: Biennial gFOBT demonstrated absolute risk reduction in CRC mortality of 0.037% in adults younger than 60 years and 0.20% in those aged 60 years or older 1.
Alternative Interval: Annual Testing
While annual FIT is also acceptable and recommended by some guidelines 1, 2, this approach:
- Increases screening burden and may reduce long-term adherence
- Generates more false-positive results requiring colonoscopy follow-up
- Is preferred by the MSTF as a tier 1 option alongside colonoscopy every 10 years
The USPSTF 2021 recommendation includes annual FIT as one of several acceptable strategies that provide reasonable balance of benefits and harms 2.
Important Clinical Considerations
Test quality matters: All stool-based tests must be performed on voided stool samples, not samples obtained by digital rectal examination 1. Single-panel office-based testing is inadequate and not recommended.
Follow-up is essential: Any positive FIT result requires timely colonoscopy follow-up. The screening program only works if patients complete diagnostic evaluation after positive results 1.
Patient adherence: The 2-year interval may be more realistic for patients who struggle with annual testing compliance. However, if a patient is unlikely to follow up biennially, consider alternative screening strategies such as colonoscopy every 10 years 1.
After recent colonoscopy: For patients who had a recent colonoscopy (within 5 years) without high-risk findings, annual FIT screening may not be necessary, as the risk of advanced neoplasia is significantly lower 3, 4.
Common Pitfall to Avoid
Do not use annual FIT after negative colonoscopy: If a patient had a complete colonoscopy within the past 5 years with no or low-risk findings, they should follow colonoscopy surveillance intervals rather than annual FIT screening. Research shows significantly lower detection rates of advanced neoplasia (3.9-6.9%) in FIT-positive patients who had recent colonoscopy compared to those without recent colonoscopy (14.8%) 3.