CT Colonography as a Triage Examination After a Positive Fecal Immunochemical Test: A Retrospective Cohort Study in a Chilean Screening Program

Colorectal cancer is a leading cause of death worldwide, affecting millions of people every year. In many places, including Chile, it is a major health challenge. The most reliable way to find and remove precancerous growths in the colon is a procedure called a colonoscopy, where a doctor uses a long, flexible tube with a camera to look inside the large intestine. However, this procedure requires specialized equipment and trained doctors, which are often in short supply. To manage this, many health programs first use a simpler, non-invasive test called a fecal immunochemical test, or FIT. This test checks a small stool sample for hidden blood, which can be a sign of a problem. When the FIT test comes back positive, it usually means the person needs a colonoscopy. But when too many people test positive, the demand for colonoscopies can overwhelm the system, creating long waiting lists and delaying care for those who need it most.

To solve this bottleneck, researchers in a region of Chile explored a different approach. They used a type of scan called computed tomography colonography, often known as virtual colonoscopy. This technique uses X-rays and computer technology to create detailed 3D images of the inside of the colon without inserting a tube. The idea was to use this scan as a filter, or triage tool, to decide which people with a positive FIT test really needed the immediate, invasive colonoscopy and which ones could wait. The goal was to see if this method could safely identify the most dangerous growths while saving the limited number of available colonoscopy slots for those who needed them most.

A team of researchers led by Francisco Navarro Subiabre and Renato Alarcón Elgueta looked back at records from a screening program in Arica, Chile, to see how well this strategy worked in real life. Between 2019 and 2022, they followed 675 people who had tested positive on the stool test. These individuals were between 45 and 75 years old and had no symptoms of cancer. Instead of sending everyone straight to a colonoscopy, the doctors first performed the virtual colonography scan on each person. The scans were then graded based on what they found. If the scan showed no significant problems or only very small growths that were unlikely to be dangerous, the person was not sent for immediate surgery. If the scan showed larger growths or suspicious signs, the person was referred for a traditional colonoscopy to confirm the findings and remove any issues.

The results showed that this filtering method worked well. Out of the 675 people scanned, about 70 percent were found to have no significant issues or only tiny growths that did not require immediate action. These people were spared the immediate need for a colonoscopy. The remaining 30 percent had findings that warranted a closer look. Of the 131 people who were referred for a colonoscopy based on the scan results, 108 had a complete and high-quality procedure. In 93 of these 108 people, the colonoscopy confirmed that the scan had correctly identified at least one growth that was 6 millimeters or larger. This means that when the scan flagged a problem, it was right about 86 percent of the time. Furthermore, the scan successfully identified 48 people who had advanced precancerous growths or cancer, which is the most critical group to catch.

The study also revealed some interesting patterns regarding who was most likely to have serious findings. Men were nearly twice as likely as women to have the high-priority results that required a colonoscopy. While the researchers noted that this observation needs further study to confirm the reasons behind it, it highlights that risk factors can vary between different groups of people. The detection rates for serious conditions in this group were significant, with the program finding advanced precancerous growths in 6.2 percent of the total group and actual cancer in 0.9 percent. These numbers are comparable to what is seen in other screening programs that rely directly on colonoscopies for everyone.

The researchers concluded that using the virtual scan as a middle step is a promising way to manage limited medical resources. By using the scan to sort patients, the program could focus its colonoscopy capacity on the people most likely to have serious disease, while safely allowing others to wait or be monitored later. However, the authors were careful to note that this was a single study in one region, and more research is needed to confirm that this approach is safe and effective over the long term, especially for the people who were told they did not need immediate surgery. They emphasized that while the scan is a powerful tool, it must be used with care and proper training to ensure no serious problems are missed. This study provides a practical example of how technology can help stretch limited healthcare resources to save more lives.