Risk of Colon Cancer with Change in Bowel Habits and Negative FIT
A negative FIT does not exclude colorectal cancer in symptomatic patients with change in bowel habits, and the decision to proceed with colonoscopy should be based on age, additional risk factors, and the presence of other alarming symptoms rather than relying on FIT results alone. 1
Understanding FIT Limitations in Symptomatic Patients
FIT is not recommended for symptomatic patients because it can delay diagnosis and is associated with increased risk of advanced-stage disease. 1 The key issue is that FIT has an 8% false-negative rate even in patients ultimately diagnosed with colorectal cancer, meaning approximately 1 in 12 cancer patients will have a negative FIT. 2
Sensitivity Data for FIT
- FIT sensitivity for colorectal cancer ranges from 73-92% depending on the test and cutoff used 1, 2
- In real-world clinical practice (not controlled trials), FIT sensitivity was 92%, meaning 8% of colorectal cancers were missed 2
- When FIT is added to symptomatic evaluation, pooled sensitivity improves to 83%, but this still means 17% of cancers could be missed 3
Age-Specific Risk Stratification
The cancer risk with change in bowel habits as an isolated symptom varies dramatically by age:
- Under 55 years: 0% colorectal cancer risk with change in bowel habits alone 4
- 55-64 years: 6% colorectal cancer risk 4
- 65-74 years: 8% colorectal cancer risk 4
- 75 years and older: 14% colorectal cancer risk 4
Clinical Decision Algorithm
Proceed Directly to Colonoscopy (Do Not Use FIT) If:
- Hematochezia (rectal bleeding) - hazard ratio 10.66 for colorectal cancer 1
- Unexplained iron deficiency anemia (ferritin <15 ng/dL) - hazard ratio 10.81 for colorectal cancer 1
- Unexplained weight loss ≥5 kg (>11 pounds) within 5 years - odds ratio 2.23 for colorectal cancer 1
- Age ≥55 years with change in bowel habits - cancer prevalence 6-14% depending on age 4
Consider Individualized Approach (FIT May Be Option) If:
- Age <55 years with isolated change in bowel habits and no other risk factors - cancer risk approaches 0% 4
- No family history of colorectal cancer 1
- No additional alarming symptoms 1
However, even in this low-risk scenario, FIT triaging remains controversial because change in bowel habits is non-specific and evidence is conflicting. 1
Critical Timing Considerations
If colonoscopy is indicated, it should be performed within 30 days of symptom presentation, with a maximum acceptable delay of 6 months. 1 Delays beyond 6 months after positive FIT increase risk with adjusted odds ratio of 1.31 for any colorectal cancer and 2.09 for advanced-stage disease. 5
Common Clinical Pitfalls
- Do not repeat FIT instead of proceeding to colonoscopy when initial FIT is negative but symptoms persist - this delays diagnosis 1
- Do not assume young age (<50 years) provides protection - early-onset colorectal cancer is rising and often presents at advanced stages 1
- Do not use FIT to triage patients with multiple symptoms - the combination of change in bowel habits plus any alarming feature warrants direct colonoscopy 1
- Do not forget that 28% of early-onset colorectal cancer patients have family history - always assess family history of all cancers 1
Bottom Line on Cancer Risk
In symptomatic patients with change in bowel habits and negative FIT:
- Overall false-negative rate: 8-17% depending on the study and population 2, 3
- Age-dependent cancer prevalence: 0% (<55 years) to 14% (≥75 years) with isolated bowel habit change 4
- Absolute cancer risk cannot be quantified from FIT alone - clinical context, age, and additional symptoms determine actual risk 1
The most important clinical action is recognizing that FIT should not be used to exclude cancer in symptomatic patients, and colonoscopy remains the diagnostic modality of choice when clinical suspicion warrants investigation. 1