Only 54% of adults who had an initial negative stool-based colorectal cancer screening test consistently repeated stool-based screening over time, according to a retrospective cohort study reported in Clinical Gastroenterology and Hepatology.
The findings highlight a practical challenge for health systems using fecal immunochemical testing (FIT) and guaiac fecal occult blood testing as colorectal cancer screening strategies. Annual stool-based screening is guideline-recommended, but its effectiveness depends on repeat testing over time.
“For those doing FIT testing, this is not a ‘one and done’ testing strategy,” said study author Ethan A. Halm, MD, MPH, MBA, of Rutgers Robert Wood Johnson Medical School. “Clinicians should encourage their patients to ‘Check your rear every year.’”
The study included 492,812 adults aged 50 to 65 years who completed a negative stool-based test in 2010 or 2011 and were eligible for repeat screening. Participants received care in four U.S. health systems participating in the National Cancer Institute–funded Population-based Research to Optimize the Screening Process (PROSPR 2) consortium: Kaiser Permanente Northern California, Kaiser Permanente Southern California, Kaiser Permanente Washington, and Parkland Health.
Investigators followed patients for up to 10 years using electronic health record, administrative, and tumor registry data. Repeat stool-based screening was categorized as consistent if patients completed testing in at least 75% of eligible screening rounds, inconsistent if they completed at least one repeat test but fewer than 75% of rounds, and no repeat screening if they did not repeat testing after the negative index test.
About half repeated testing consistently
Overall, 54% of patients were consistent repeaters, 30% were inconsistent repeaters, and 16% never repeated stool-based screening. Patients completed a median of four stool-based tests over a median follow-up of 6.5 years.
“In this study of nearly half a million patients who had a negative stool test for colorectal cancer screening (FIT or FOBT), only slightly more than half repeated the test every year as recommended, about one-third repeated it inconsistently, and 1 in 6 did not repeat it,” Dr. Halm said.
Adherence varied substantially by health system. Kaiser Permanente Northern California had the highest proportion of consistent repeaters, at 61%, followed by Kaiser Permanente Southern California at 50%, Kaiser Permanente Washington at 25%, and Parkland Health at 5%. The proportion of never repeaters ranged from 12% at Kaiser Permanente Northern California to 54% at Parkland Health. In multivariable analyses, health system was the strongest predictor of consistent screening.
“The health system where patients received their care had the strongest impact on consistent adherence with 20-fold variation by site even after adjusting for other patient factors,” Dr. Halm said. “Health systems with the most organized mailed stool-test outreach programs had higher rates of consistent screening.”
Several patient-level factors also were associated with consistent repeat screening, including older age, male sex, non-Hispanic white race, lower comorbidity, body mass index below 25 kg/m2, public insurance, prior stool-based testing, and a primary care visit in the year before the index test. Prior stool-based testing was one of the strongest patient-level predictors, more than doubling the adjusted odds of consistent adherence.
Screening consistency was tied to cancer stage
Among 1,829 incident colorectal cancer cases, stage at diagnosis differed by screening consistency. Distant-stage disease was more common among never repeaters, at 18.1%, compared with 11.8% among inconsistent repeaters and 11.2% among consistent repeaters.
Local-stage cancer was more common among patients who repeated screening, occurring in 51.8% of consistent repeaters and 46.6% of inconsistent repeaters, compared with 42.2% of never repeaters.
“More consistent CRC screening can reduce the chance of distant cancer and save more lives,” Dr. Halm said.
For clinicians, the results reinforce that stool-based screening programs cannot be judged only by the first completed test. A negative FIT or fecal occult blood test should be treated as the start of a recurring screening pathway, not a completed screening episode.
Dr. Halm said the findings also show the limits of relying only on office-based reminders. “Relying just on a primary care provider (PCP) to recommend cancer screening, on patients coming to see their PCP yearly, and/or visit-based screening reminders in the electronic health record, is not enough to prevent distant stage, harder to cure colorectal cancer,” he said.
Limitations and next steps
The study had several limitations. Not all patients had 10 years of observation time because of disenrollment or the end of the study period. The cohort included patients who began with stool-based screening and did not reflect the total proportion of adults who were up-to-date with colorectal cancer screening by any method.
“The study did not include people who started with colonoscopy-based screening, so our results do not reflect the total proportion of individuals who were up-to-date with CRC screening from all screening modalities,” Dr. Halm said.
However, he noted that patients who crossed over to colonoscopy were censored from subsequent analyses so they were not counted as inconsistent or never repeaters. The study was also conducted before wide availability of newer home multitarget stool FIT/DNA tests, such as Cologuard, and Dr. Halm said more research is needed to assess repeat testing patterns with those newer tests.
The findings support a health-system approach to stool-based colorectal cancer screening, with attention to longitudinal adherence rather than one-time uptake. For screening programs, annual stool-based testing requires infrastructure: reminders, mailed outreach, primary care engagement, tracking, and systems to identify patients who miss repeat rounds.
The authors reported no conflicts of interest. The study was funded by the National Cancer Institute Population-based Research to Optimize the Screening Process consortium.