CT Colonography Found Superior to Stool DNA Testing for Colorectal Cancer Screening

A new study published in Radiology, the journal of the Radiological Society of North America (RSNA), has concluded that CT colonography outperforms stool DNA testing in both cost and clinical effectiveness for colorectal cancer screening.

Colorectal cancer ranks as the second most deadly cancer worldwide. Regular screening of the colon and rectum helps in the early detection and removal of precancerous polyps, thereby reducing the likelihood of late-stage cancer diagnoses and the accompanying treatment costs.

With an increasing number of colorectal cancer cases emerging among younger populations, health authorities—including the U.S. Preventive Services Task Force—have lowered the recommended age for initial screening to 45.

“In the U.S., conventional colonoscopy remains the dominant screening test for colorectal cancer, despite the fact that it is the most expensive and invasive option,” said Dr. Perry J. Pickhardt, the John R. Cameron Professor of Radiology and Medical Physics at the University of Wisconsin School of Medicine and Public Health.

While colonoscopy continues to be the standard due to its ability to remove precancerous growths during the procedure, less invasive and lower-cost alternatives have gained traction, especially with recent expansions in Medicare coverage. These include multitarget stool DNA (mt-sDNA) testing, which detects cancer markers in stool, and CT colonography, a CT-based imaging procedure that scans for polyps and tumors.

Dr. Pickhardt emphasized that both alternatives are “less invasive and much safer primary screening options.” To determine which offers greater value, he and his team directly compared mt-sDNA and CT colonography in terms of effectiveness and cost efficiency.

Using a Markov model to simulate outcomes in 10,000 individuals starting at age 45, the researchers modeled disease progression and screening outcomes through age 75, assuming perfect compliance with recommended screening and follow-ups.

Without screening, 7.5% of participants were projected to develop colorectal cancer—consistent with broader population data.

Both methods substantially reduced cancer risk, but CT colonography led to a higher reduction—between 70% and 75%—compared to mt-sDNA’s 59% reduction.

Cost-effectiveness was measured using Quality-Adjusted Life Years (QALY), with one QALY representing one year in perfect health. While mt-sDNA was considered cost-effective at roughly $9,000 per QALY (well below the $100,000 benchmark), CT colonography was determined to be outright cost-saving.

The researchers also explored a hybrid screening strategy, focused on managing small colorectal polyps (6–9 mm) with three-year CT colonography surveillance, and referring only larger polyps (≥10 mm) for colonoscopy. This approach showed the most favorable balance between effectiveness and cost.

In contrast, the standard CT colonography protocol—referring all polyps ≥6 mm for colonoscopy—was not cost-effective relative to the hybrid approach, primarily due to the high costs of follow-up colonoscopies for smaller, lower-risk polyps without sufficient health benefit to justify the expense.

“Among the safe, minimally invasive colorectal cancer screening options, CT colonography is more effective at preventing and detecting cancer—and is also more cost-effective—than stool DNA testing,” Dr. Pickhardt stated. “Furthermore, CT colonography can provide for extracolonic screening for things like osteoporosis and cardiovascular disease.”