About 60 percent of Americans aged 50 or older who are at average risk for colorectal cancer - some 42 million people - have not yet been screened, researchers report.

Catching up on the backlog of unscreened people presents a challenge.

Dr. Laura C. Seeff, at the Centers for Disease Control and Prevention (CDC) in Atlanta, and her associates analyzed data from the US Census Bureau and the CDC’s National Health Interview Survey.

Their results, in the medical journal Gastroenterology, show that 41.8 million people age 50 and older have not been screened for colorectal cancer.

Meanwhile, data from the national Survey of Endoscopic Capacity suggest that an additional 15 million sigmoidoscopies or colonoscopies could be performed. If half of that capacity were used for screening, it could take up to 10 years to screen everyone who should be.

However, if people first performed a blood-in-stool test, and then only those with positive results had a definitive colonoscopy, screening the entire population could be accomplished within 1 year.

In an editorial, Dr. Theodore R. Levin points out that the 10-year estimates do not take into account a number of factors, including “tests needed to keep the currently screened population up to date on screening, or an increase in the 50- to 80-year-old population during the 10 years of trying to provide universal screening.”

One important measure that should be taken, he suggests, is to avoid excessive, unnecessary examinations.

He recommends less frequent screening for patients younger than 50 to 65 years, using colonoscopy primarily for older patients.

SOURCE: Gastroenterology, December 2004.