Clinical Context

The most common screening method for colorectal cancer (CRC) is the colonoscopy in the US. While it remains the gold-standard, it comes with barriers which may prevent a patient from access to this method of screening completely. Challenges may include the bowel preparation process, accessibility to a healthcare center that provides the procedure, or concerns with sedation and after-care. Due to these reasons, clinicians may need to consider non-colonoscopy options such as non-invasive at-home stool-based tests (SBTs). Two types include fecal immunochemical tests (FITs), which use antibodies to detect blood in the stool, and multitarget stool DNA (mt-sDNA) tests, which use antibodies to detect blood in stool and then identify DNA biomarkers that are associated with CRC^[1]. Guiac-based fecal occult blood test (gFOBT) is also a SBT; however, it is less accurate and requires dietary changes prior to collecting the sample^[2].

Stool-based tests are a relatively inexpensive and simple means to screen for CRC among average-risk adults, but how accurate are these tests? A previous study by Lee and colleagues, which was published in the February 4, 2014 issue of the Annals of Internal Medicine,^[3] assessed this issue in a meta-analysis of 19 studies. They found the overall diagnostic accuracy of the FIT tests to be 95%. Exclusion of discontinued FITs improved the homogeneity of results. Testing for multiple stool samples in a single test window failed to improve diagnostic accuracy compared with a singular sample.

The mt-sDNA test has an overall diagnostic accuracy of 92%; however, clinicians should note that these tests do return more false positives than FIT tests. It is suggested the mt-sDNA test be completed once every 3 years^[2].

Of course, accurate SBTs are only valuable when they are routinely partnered with colonoscopy in the event of a positive test. The current study by Mohl and colleagues evaluates the rate of completed colonoscopy after positive SBTs as well as variables associated with lower rates of follow-up colonoscopy.

Study Synopsis and Perspective

Nearly half of people with a positive stool test result do not get a potentially lifesaving, follow-up colonoscopy, according to a new study.

Researchers said that clinicians "were uniformly surprised” that their patients did not seek follow-up care.

"Obviously, that's a huge problem," study-co-author Jeff Mohl, PhD, director of research and analytics for the American Medical Group Association, told HealthDay.^[4] "If you're trying to estimate how many lives are saved, you're assuming that everyone gets follow-ups if they have a positive result, and if half of them don't do that, obviously you'll only save half as many people."

Stool tests are 71% to 92% accurate depending on screening type, according to the Cleveland Clinic.^[4] Early detection is important: When CRCs are found early, 90% of people live at least another 5 years. 

The study was published this month in JAMA Network Open.^[1] Researchers analyzed data for 32,769 people aged 50 to 75 years who received a positive stool-based screening test result between January 2017 and June 2020.

Overall, 56% of people scheduled follow-up colonoscopies within 1 year. The clinicians of the patients who did not get colonoscopies said perceived discomfort of the procedure may have played a role in their patients' decisions. 

Colonoscopies screen for CRC and potentially precancerous polyps. The procedure is typically done on an outpatient basis, lasts about an hour, and requires dietary adjustments and taking a laxative beforehand.

People should begin colorectal screenings starting at age 45 years, according to guidelines^[6] from an independent panel. People with average risk levels can first do stool-based screening tests like those involved in the study.

Researchers found that the likelihood of scheduling a follow-up colonoscopy was impacted by a person's race, ethnicity, insurance type, and the type of screening they used (fecal immunochemical tests or multitarget stool DNA [mt-sDNA]). Socioeconomic factors and the COVID-19 pandemic were significantly associated with lower follow-up rates.

Study authors noted that few health systems tracked whether patients got a colonoscopy after a positive stool result and recommended prioritizing the backlogs.

Clinical Implications

• A previous meta-analysis by Lee and colleagues found that the rates for sensitivity, specificity, and overall diagnostic accuracy of FIT for CRC screening was 95%. Assessing multiple stool samples in a single screening window failed to improve diagnostic accuracy. A separate source found mt-sDA tests to have a diagnostic accuracy of 92%.
• The current study by Mohl and colleagues finds that the rate of colonoscopy within 360 days of a positive stool test among adults at average risk for CRC is 56%. Black and Asian adults were less likely to receive colonoscopy, as were adults with high comorbidity levels and adults who received FIT vs mt-sDNA tests.
• Implications for the healthcare team: The healthcare team should follow rates of colonoscopy after positive stool testing to improve detection rates for CRC and work with institutional resources to create pathways for better follow-up and referral.

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