About 23 million American adults have failed to receive the recommended screening for colorectal cancer (CRC), according to a report today from the Centers for Disease Control and Prevention (CDC). However, researchers say people are more likely to get the potentially lifesaving tests if they are offered a choice of methods.

The proportion of U.S. adults who are up to date with their recommended CRC screenings increased from 54 percent in 2002 to 65 percent in 2012, according to the report. Researchers attribute this to an increased use of colonoscopies, in which a physician uses a flexible, lighted tube to search the rectum and entire colon for polyps and cancers – many of which can be removed during the procedure.

But during the same 10-year time period, two other recommended tests declined in use: sigmoidoscopy and high-sensitivity fecal occult blood testing (FOBT). A sigmoidoscopy is similar to a colonoscopy, but the doctor performing it uses a shorter tube to examine the rectum and lower third of the colon. With FOBT, a patient collects a small stool sample at home and mails it to a laboratory to test for traces of blood.

Many doctors recommend colonoscopy to their patients because it provides the most complete view of the colon. But it's also the most invasive of the recommended CRC tests and requires patients to undergo a strict diet the day before screening to help empty the colon.

Research suggests patients who choose FOBT are more likely to complete the test than those who choose colonoscopy. Therefore, federal health officials suggested that doctors offer all recommended CRC tests and identify a screening strategy that their patient is most likely to follow.

Rather than viewing colonoscopy as a rite of passage for everyone reaching their 50th birthday, researchers believe more adults will get screened for CRC if they're encouraged to choose from a menu of strategies.

The U.S. Preventive Services Task Force recommends three screening options for adults in the 50 through 75 age bracket. The first option simply involves undergoing FOBT every year. The second option involves undergoing a colonoscopy every 10 years. The third option combines a sigmoidoscopy every five years with FOBT every three years.

Among adults who are up to date on their recommended CRC screening, 62 percent use colonoscopy, according to the CDC report. Just over 10 percent use FOBT, and less than 1 percent use a combination of sigmoidoscopy and FOBT.

"If someone has a strong family history of colon cancer or has polyps or a personal history of a disease such as inflammatory bowel disease, then colonoscopy is clearly preferred," said Dr. Tom Frieden, director of the CDC. "However, for everyone else – and that's the great majority of people – there is no proven benefit of one versus the other approach."

Frieden added that the tests are not completely unrelated. For example, patients whose stool samples test positive for blood through FOBT are generally referred to undergo colonoscopies as a follow-up procedure.

Colorectal cancer claims approximately 50,000 lives in the United States each year and is the leading cause of cancer deaths among nonsmokers. However, public health officials say many of these lives could be saved through early detection if more people selected a screening plan and followed through with it.

"The best test is the test that gets done," Frieden said.