The American College of Gastroenterology (ACG) has just released new guidelines for colorectal cancer screening — the first update to their last recommendations issued in 2000.

One key change is that screening tests are now divided into those designed to prevent colorectal cancer and those designed to detect the cancer. Prevention screening is preferred over early detection, the ACG states.

The best colorectal cancer prevention test is still colonoscopy, according to the guidelines which appear in The American Journal of Gastroenterology for March.

The prior recommendation that screening colonoscopy be performed every 10 years starting at age 50 years still stands with one modification: screening should begin at age 45 for African American men.

This change was prompted by recent research showing increased rates of polyps and colorectal cancer in this population, Dr. Douglas K. Rex, from Indiana University Medical Center, Indianapolis, and the guideline developers state. Polyps are abnormal growths in the colon, which can sometimes be a precursor to the development of cancer.

The new guidelines state that virtual colonoscopy, also known as CT colonography, is not as effective as traditional colonoscopy in detecting small lesions and carries an unclear radiation risk; therefore, it should only be considered in subjects who refuse standard colonoscopy. If selected, CT colonography should be performed every 5 years.

Virtual colonoscopy involves taking numerous X-rays of the colon, which are then fed into a computer. The computer reconstructs the images to generate a three-dimensional picture of the colon, much like what is seen with standard colonoscopy. Because virtual colonoscopy does not require the insertion of a long camera tube into the anus, patients typically tolerate it better than standard colonoscopy.

Other alternatives for patients refusing colonoscopy include flexible sigmoidoscopy, a less invasive version of colonoscopy, performed every 5 to 10 years, and annual fecal immunochemical blood test, the preferred detection test.

The guidelines also address bowel cleansing for colonoscopy, to improve tolerability and screening rates, as well as the quality of the examination. It is recommended that bowel preparations be given as a split dose, meaning that half is given the day before and half on the day of the procedure.