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People receiving blood-based colorectal screening tests showed disappointingly low rates of receiving follow-up colonoscopies that are essential when tests are abnormal, with follow-up rates as low as some reported with stool sample tests, according to results from a real-world study.

“To our knowledge, no previously published studies have directly examined follow-up colonoscopy rates after abnormal blood-based colorectal cancer screening,” said Timothy A. Zaki, MD, a senior gastroenterology fellow at UCLA Health and first author of the study published in Gastroenterology.

“There was certainly hope that blood-based screening would lead to better follow-up adherence,” Zaki told Medscape Medical News. “However, our findings suggest that the need for a follow-up colonoscopy remains a major barrier — regardless of the initial screening method,” he said.

With colorectal cancer representing the second leading cause of cancer-related deaths in the US, early screening is highly recommended; however, barriers ranging from fear of results, or of the process itself, to uninsured status prevent many from receiving either the gold standard test of colonoscopy or even the less burdensome stool-based screening.

Blood-based screening tests meanwhile, in addition to being less burdensome, have shown high screening accuracy, with the FDA-approved test Shield (Guardant Health) shown to have an 83% sensitivity for colorectal cancer and a 90% specificity for advanced neoplasia.

However, failing to receive the needed follow-up colonoscopy if test results are abnormal almost defeats the test’s purpose. Follow-up rates reported in some studies regarding abnormal stool-based tests show results well below optimal levels, some falling in the 50%-60% range.

To evaluate follow-up rates with blood-based tests, Zaki and his colleagues conducted a retrospective analysis, evaluating de-identified records from Guardant Health and clinical data from an administrative claims database of 6068 average-risk patients in the US who received the blood-based Shield screening test in primary care settings between May 2022 and September 2024.

Of the patients (mean age, 63 years), 37.8% were non-Hispanic White, 7.0% were non-Hispanic Black, 6.5% were non-Hispanic Asian or Pacific Islander, 16.5% were Hispanic, and 32.2% were of other or unknown race or ethnicity.

Overall, 7.4% (n = 452) received an abnormal test result, and in an analysis of 50.4% (n = 228) of patients who had administrative claims data for 6 months of follow-up, only 49% received a follow-up colonoscopy within 6 months, with a mean time to the colonoscopy of 66.4 days.

A somewhat higher proportion (56% [n = 128]) of patients received a follow-up colonoscopy at any time, with a mean time to the colonoscopy being 98.3 days among the overall population who received the follow-up.

Further analysis of 27% (n = 121) of patients who had 12 months of follow-up after an abnormal test showed that a somewhat higher proportion (58% [n = 70]) of patients received a follow-up colonoscopy at any time after the test, and 55% (n = 67) received the colonoscopy within 12 months.

Overall, 42% (n = 51) of those patients did not receive a follow-up colonoscopy after the abnormal Shield test.

Among the strongest factors associated with failing to receive a follow-up colonoscopy within 6 months was having Medicare Advantage vs having private insurance (adjusted odds ratio [aOR], 0.26), while factors associated with a greater likelihood of follow-up included having fewer comorbidities (aOR, 0.90).

The significantly lower rate of follow-up with Medicare Advantage was especially notable, Zaki said.

“This is one of the more striking findings of the study,” he said. “While we can’t determine the exact reasons from claims data alone, several factors could be at play, including network restrictions, prior authorization requirements, higher cost-sharing under certain Medicare Advantage plans, or barriers specific to the types of people more likely to have Medicare Advantage.”

“These potential barriers may make it harder for patients to access timely colonoscopy after an abnormal test result,” he added.

The study conversely showed a lack of any significant association between follow-up and factors including race, which was also notable, considering other recent research showing lower rates of follow-up among Black and Hispanic patients receiving stool-based testing.

“This difference may be due to variations in healthcare access, system-level factors, or patient populations that have access to, select, or adhere to blood-based screening in these studies,” the authors explained in the study.

The 49% rate of follow-up colonoscopy at 6 months is nearly the same as the 48% reported with stool-based screening in a recent study also using national claims data.

Notably, however, higher follow-up rates to stool-based tests have been reported in Veterans Affairs (62.1%) and some integrated health systems (81%) populations, the authors said.

Key limitations of the study include that Medicare fee-for-service claims were not available, which likely resulted in data from a relatively younger cohort and a lower rate of positive screenings, which was 7% vs 11.4% in a registrational study, the authors noted.

Furthermore, the use of closed claims likely could have resulted in missing colonoscopies that were completed but not yet reimbursed or those that were scheduled but not yet billed, they added.

“As a result, our observed follow-up colonoscopy rate may underestimate the true follow-up rate,” the authors said.

However, the use of closed claims likely ensured reliable colonoscopy data, they noted.

In terms of efforts to improve patient follow-up rates, a colorectal cancer screening completion measure has been proposed to complement the existing Healthcare Effectiveness Data and Information Set measure, which would recommend additional tracking of patients with abnormal blood or stool tests through the second step of whether those with an abnormal result received a follow-up colonoscopy.

Such a measure “would encourage systems and payers to track whether patients with abnormal noninvasive tests actually complete a diagnostic colonoscopy within a recommended time frame,” Zaki said.

“Having a metric will also encourage health systems to implement interventions to increase follow-up rates and help shift the focus from screening alone to the full continuum of care.”

Other strategies showing benefits in improving follow-up include multifaceted interventions that integrate patient navigation, reminder systems, and strong clinician recommendation, Zaki noted.

The current study meanwhile adds important real-world evidence to the research, “using recent national claims data from a large and diverse population, helping to fill a critical gap in the literature,” Zaki said.

Ultimately, “blood-based colorectal cancer screening is promising, but it only works if individuals complete the follow-up colonoscopy,” said the study’s senior author Folasade P. May, MD, an associate professor of medicine at the David Geffen School of Medicine at UCLA, in a press statement.

“More efforts are needed to help patients follow through to actually diagnose and treat the disease.”

Physicians, Colonoscopists Key in Solving the Problem

Commenting on the study, Theodore R. Levin, MD, a research scientist at the Kaiser Permanente Division of Research, Pleasanton, and gastroenterologist with Kaiser Permanente, Oakland, both in California, noted that the findings “are concerning but not surprising.”

“In the absence of a formal process to track patients with a positive stool-based screening test, we typically find fewer than half of people with a positive stool test go on to get a colonoscopy,” he told Medscape Medical News.

“I would expect the numbers to be even lower for blood-based screening tests because this is a group that is likely to be less willing to have a colonoscopy.”

Levin agreed that the use of claims data has key limitations, including potentially undercounting colonoscopies and lacking important context on reasons follow-up colonoscopies were missed.

Nevertheless, the findings underscore that “failure to obtain a follow-up colonoscopy after a positive noninvasive test remains an ongoing challenge,” he said.

“Responsibility for solving this problem lies with the physicians ordering the tests and for the colonoscopists who receive the referral.

“Such patients should be prioritized in the physicians’ scheduling queue,” he added.

“There is no way to know how your patients are doing unless you have a way to track them to colonoscopy completion.”

Zaki had no disclosures to report. The remaining authors’ disclosures are detailed in the published study. Levin reported receiving research support from Freenome and serving as an advisor to Geneoscopy.