What Happens After a Positive Stool Test

Colorectal cancer screening is having a genuine moment. More people are completing a first screening test today than at almost any point in the last decade, and stool-based testing deserves real credit for that. Fecal immunochemical tests (FIT) and multi-target stool DNA tests have made the first step dramatically easier: no bowel prep, no clinic visit, just a sample collected at home. The market is voting with real capital. Abbott completed its acquisition of Exact Sciences, the maker of Cologuard, in a deal valued at roughly $21B dollars, and Cologuard Plus launched as the next generation of that technology. This is a screening tool that is working exactly as designed.

The data backs this up. In the landmark NEJM trial comparing colonoscopy to FIT as a primary screening strategy, participation was meaningfully higher in the FIT arm than the one-time colonoscopy arm, 34.2% versus 24.6%. Lower the barrier to the first step, and more people take it. That is the whole point of stepped screening, and it is working.

But a positive stool test is not a diagnosis. It is a referral. Anyone who screens positive on a FIT or stool DNA test still needs a colonoscopy to find out what the result actually means, whether that is a polyp, an early cancer, or nothing at all. The US Multi-Society Task Force on Colorectal Cancer sets an 80% target for how many of those patients should complete that follow-up colonoscopy in a timely way.

Real-world numbers fall well short of that target, and not in just one study. A JAMA Network Open analysis across multiple health care organizations found a median follow-up colonoscopy completion rate of 53.4% within one year. A federally qualified health center study found that while 90% of FIT-positive patients were referred to colonoscopy, only 43% completed one within a year, with a median wait of 83 days. A large claims-based analysis found completion at 12 months ranged from 35.2% percent for FIT patients up to 85.0% for stool DNA patients, a gap wide enough to suggest the test type itself shapes what happens next.

This is not a failure of stool testing. It is a gap between two tools that each do their individual job well, and a system that has not yet closed the space between them. The consequences of that gap are real. Patients with a positive stool test who never complete a follow-up colonoscopy face a 1.8 times higher risk of colorectal cancer over six years.

So why do patients stall at exactly the moment they are closest to an answer? Among FIT-positive patients who did not complete follow-up, one university hospital study found that patient hesitancy was the single most common reason, cited in 35.2% of cases, and that this hesitancy was attributed primarily to the burden of bowel preparation, along with concerns about sedation and pain. This tracks with a broader, well-established pattern. A survey of colonoscopy patients found that 71% named bowel preparation as the worst part of the experience, and 55% named it as the factor most likely to deter them from a future colonoscopy.

Put plainly, patients are not skipping the most important step in their own cancer screening because they stopped caring. They are responding, rationally, to a step in the process that is genuinely unpleasant, at the exact moment their anxiety about a possible diagnosis is highest.

This is the part of the pathway Zera Medical is focused on. Better front-door screening tools like FIT and stool DNA testing, and a better experience at the colonoscopy prep stage, are not competing solutions. They are two pieces of the same problem: getting patients all the way through a screening pathway that only works if every step gets completed.

Wider adoption of stool-based screening should be good news for everyone working on colorectal cancer prevention. It means more people are arriving at that all-important second step. The work now is making sure fewer of them turn back once they get there.

This post is part of an ongoing educational series from Zera Medical on the colorectal cancer screening gap and the preparation experience that shapes it. Zera Medical is developing ZeraFlow™, an investigational clinic-based bowel preparation system currently under FDA regulatory review. ZeraFlow has not been cleared or approved by the U.S. Food and Drug Administration and is not available for commercial distribution or sale.