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After the screening age for colonoscopy was lowered in colorectal cancer (CRC) guidelines, younger people were more likely to undergo the procedure, researchers found.

Among people ages 45 to 49, first-time screening rates increased from 3.5% in the period before guidelines were changed to 11.6% after they were updated (relative rate [RR] 3.36, 95% CI 2.45-4.61), reported Uri Ladabaum, MD, MS, of Stanford University School of Medicine in Redwood City, California, and colleagues in .

During this time period, the 45-49 and 50-54 age groups showed similar detection rates at first-time screening:

• Adenomas: 34.3% vs 38.2%
• Advanced adenomas: 6.3% vs 5.8%
• Sessile serrated lesions (SSLs): 8.6% vs 9.4%
• Advanced SSLs: 2.9% vs 3.0%
• Mean number of adenomas per colonoscopy (APC): 0.58 vs 0.63
• Mean number of lesions per colonoscopy (LPC): 0.69 vs 0.76

These rates were similar to the 60-64 age group at re-screening: 33.4%, 6.1%, 7.2%, 2.3%, 0.61, and 0.70, respectively.

Furthermore, all detection rates, APC, and LPC increased from before the guidelines were changed (October 2017 to December 2018) to after they were updated (January 2019 to August 2021), with the overall adenoma detection rate increasing from 35.1% to 42.6% at first-time screening among all people ages 45 to 49 (P<0.0001).

First-time colonoscopies were still largely performed in patients ages 50 to 54 in both time periods, while re-screening colonoscopies showed a shifting trend toward older ages. Patients ages 60 to 64 were the most likely to undergo re-screening during both time periods, Ladabaum and team noted.

"In the early contemporary era of updated CRC screening guidelines, screening colonoscopy volume among 45-49 year-old patients has increased modestly, and lesion detection rates in 45-49 year-old patients have not decreased as might have been seen if low-risk persons were self-selecting for screening," they concluded.

Guidelines from the in 2018 and the U.S. Preventive Services Task Force in 2020 lowered the endorsed CRC screening age after rising CRC incidence among younger people, the authors noted. Prior studies have supported the update, but not all colonoscopies were completed prior to the update, nor were all participants at average risk.

"The [new] study supports more recent recommendations that colonoscopies should start at the younger age of 45, rather than the previously adhered to 50-years-of-age standard," said Allen Kamrava, MD, of Cedars-Sinai Medical Center in Los Angeles, who was not involved in this study. "Having matched the pathologic results, it provides a more compelling narrative that earlier screening is indeed warranted."

"Ongoing national monitoring is needed to fully assess the impact of the updated guidelines," Ladabaum and colleagues wrote.

The team used the Colonoscopy Quality Assurance Program, which contains data on all colonoscopies performed at four endoscopy units in different geographic locations. They included 7,990 patients who had undergone colonoscopies from October 2017 through August 2021: 4,266 first-time colonoscopies and 3,724 re-screening colonoscopies. Median age of patients was 56-58, and over half were women.

Only colonoscopies with adequate bowel preparation -- as evidenced by a Boston bowel preparation score ≥2 in each segment -- and extent of examination to the cecum were included.

The authors acknowledged that their findings were based on a single healthcare system and may not be generalizable to others. Furthermore, their routine audit process was not designed to confirm CRC detection.

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