Currently five types of screening are available for detecting colorectal cancer (CRC). One of those, the FOBT, is used to find occult (hidden) blood in feces. People will receive a test kit with instructions at their doctor?s office that explain how to take a stool sample at home. The kit is then returned to the doctor's office or a medical laboratory for testing. According to the ACS, a single test of a stool sample (such as that done during a digital rectal exam, or DRE, in a doctor's office) is not an adequate substitute for the home testing kit.

Hidenori Nakama, MD, from the Shinshu University School of Medicine in Matsumoto, Japan, and his colleagues, compared the ability of a FOBT to predict colon cancer in two groups of 522 people, using either self-collected stool or stool collected in a doctor's office by DRE.

In the self-collected stool group, 20 had a positive FOBT indicating the presence of pre-cancerous or cancerous cells. Of the 20 positive tests, 60% were confirmed to be accurate with a colonoscopy. In contrast, in the DRE group, 49 were positive, but only 26.5% were confirmed to be accurate with a colonoscopy, indicating that DRE is not as accurate as self-collection for an FOBT sample. The authors conclude that DRE stool samples were often falsely positive, perhaps because of the way the specimen is collected. This led to unnecessary colonoscopies.

The authors also point out that other disorders including diverticulosis, (an outpocketing of the colon, which can become inflamed), bleeding from the colon, and hemorrhoids may also contribute to positive results for FOBT. A more accurate test, such as a colonoscopy, should confirm positive results from an FOBT.

Anne Chao, PhD, a research scholar in the ACS?s department of epidemiology and surveillance research notes that persons taking the FOBT also should avoid certain medications or foods to prevent false positive test results, such as:

• Non-steroidal anti-inflammatory drugs (such as ibuprofen, naproxen, or aspirin (more than one adult aspirin per day) for seven days prior to testing
• Vitamin C in excess of 250 mg from either supplements or citrus fruits and juices for three days before testing
• Red meats for three days before testing

"The American Cancer Society recommends collecting and testing six samples from three consecutive stools at home, based on the fact that colon cancer or precancerous cells usually bleed intermittently, and that blood is usually not present throughout the entire stool," Chao says. "It is important to be screened for colorectal cancer with FOBT using a test kit that allows one to collect several samples from stool, rather than one sample from a doctor's DRE," she adds.

The study supports the ACS? stance. "These data indicate that stool samples obtained by digital rectal exam should not be considered as the preferred method of stool sampling for FOBT," the authors note.

Beginning at age 50, most men and women should follow one of the five screening options below:

• Yearly fecal occult blood test (FOBT)*, or 
• Flexible sigmoidoscopy every 5 years, or 
• Yearly fecal occult blood test plus flexible sigmoidoscopy every 5 years* (Of the three options above, the American Cancer Society prefers yearly FOBT combined with flexible sigmoidoscopy, an examination of the lower third of the colon that searchers for precancerous and cancerous cells, every 5 years), or
• Double contrast barium enema every 5 years, or 
• Colonoscopy every 10 years

*For FOBT, the take-home multiple sample method should be used.

People who are at an increased or higher risk should talk with a doctor about a different testing schedule.