Time to colonoscopy after abnormal stool-based screening and risk for colorectal cancer incidence and mortality

Background and aims

The optimal time interval for diagnostic colonoscopy completion after an abnormal stool-based colorectal cancer (CRC) screening test is uncertain. We examined the association between time to colonoscopy and CRC outcomes among individuals who underwent diagnostic colonoscopy after abnormal stool-based screening.


We performed a retrospective cohort study of Veterans age 50-75 years with an abnormal fecal occult blood test (FOBT) or fecal immunochemical test (FIT) between 1999 and 2010. We used multivariable Cox proportional hazards to generate CRC-specific incidence and mortality hazard ratios (HRs) and 95% confidence intervals (CI) for 3-month colonoscopy intervals, with 1-3 months as the reference group. Association of time to colonoscopy with late-stage CRC diagnosis was also examined.


Our cohort included 204,733 patients. Mean age was 61 years (SD: 6.9). Compared to patients who received a colonoscopy at 1-3 months, there was an increased CRC risk for patients who received a colonoscopy at: 13-15 months (HR=1.13, 95%CI:1.00-1.27), 16-18 months (HR=1.25, 95%CI:1.10-1.43), 19-21 months (HR=1.28, 95%CI:1.11-1.48), and 22-24 months (HR=1.26, 95%CI:1.07-1.47). Compared to patients who received a colonoscopy at 1-3 months, mortality risk was higher in groups who received a colonoscopy at: 19-21 months (HR=1.52, 95%CI:1.51-1.99) and 22-44 (HR=1.39, 95%CI:1.03-1.88). Odds for late stage CRC increased at 16 months.


Increased time to colonoscopy is associated with higher risk of CRC incidence, death, and late stage CRC after abnormal FIT/FOBT. Interventions to improve CRC outcomes should emphasize diagnostic follow-up within 1 year of an abnormal FIT/FOBT result.

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