BackgroundFor colorectal cancer (CRC) screening to improve survival, patients with an abnormal fecal immunochemical test (FIT) must follow-up with a diagnostic colonoscopy. Adherence to follow-up is low and patient-level barriers for suboptimal adherence have yet to be explored.ObjectiveTo characterize barriers for non-completion of diagnostic colonoscopy after an abnormal FIT reported by under- and uninsured patients receiving care in a safety-net health system.DesignA longitudinal, cohort study of CRC screening outreach to 8565 patients using mailed FIT kits. Patients with abnormal FIT results received telephonic navigation to arrange for a no-cost diagnostic colonoscopy.PatientsAdults aged 50-64 years receiving care at a North Texas safety-net health system.ApproachDescriptive analyses characterized the patient sample and reasons for lack of follow-up after abnormal FIT over the 3-year outreach program. Thematic qualitative analyses characterized reasons for lack of follow-up with a colonoscopy after the abnormal FIT.Key resultsOf 689 patients with an abnormal FIT, 45% (n = 314) did not complete a follow-up colonoscopy. Among the 314 non-completers, 184 patients reported reasons for not completing a follow-up colonoscopy included health insurance-related challenges (38%), comorbid conditions (37%), social barriers such as transportation difficulties and lack of social support (29%), concerns about FIT/colonoscopy process (12%), competing life priorities (12%), adverse effects of bowel preparation (3%), and poor health literacy (3%). Among the 314 non-completers, 131 patients did not report a barrier, as 51% reported that that had completed a previous colonoscopy in the past 10 years, 10% refused with no reason, and 10% were never reached by phone.ConclusionsFuture studies aimed at improving FIT screening and subsequent colonoscopy rates need to address the unique needs of patients for effective and sustainable screening programs.Trial registrationNCT01946282