The Role of Fecal Occult Blood Testing in Colorectal Cancer Screening

Credit: NCI

Credit: NCI

Each year nearly 150,000 people in the U.S. are diagnosed with colorectal cancer and around 50,000 die from the disease. Studies have shown that when performed every one to two years in people ages 50 to 80, fecal occult blood tests (FOBT) can help reduce the number of deaths from colorectal cancer by 15 to 33 percent. Although various screening methods, including FOBT, have been available for decades and new techniques continue to be developed, colorectal cancer screening rates remain lower than hoped for.

Fecal occult blood tests are the most affordable and least invasive of the various screening tests available for colorectal cancer. Prior to 2001, FOBT was one of the most widely used screening tests for colorectal cancer.  In recent years, FOBT use has been surpassed by colonoscopy.  Reasons for this shift were discussed at a recent NIH State-of-the-Science Conference on Colorectal Cancer Screening.

FOBT tests check for blood in fecal matter by requiring patients to place a small sample of stool on a chemically treated card, pad, or cloth wipe. A positive result leads to a chemical reagent on the material turning blue, indicating that there is blood in the stool sample. Currently, two types of FOBT can be used for detecting occult blood in stool—the guaiac based (chemical test) and an immunochemical test (antibody-based test).

The first, guaiac FOBT, which costs about five dollars, uses the chemical guaiac to detect heme in stool. Heme is the iron-containing component of the blood protein hemoglobin. The second, immunochemical FOBT, also referred to as fecal immunochemical testing (FIT), uses antibodies to detect human hemoglobin protein in stool. Antibodies are proteins generally found in the blood that detect and destroy invaders such as bacteria. The cost of this test is approximately $22. Both tests are commonly completed at home and then submitted to a lab for analysis, with results reported back to the patient and physician within days.

Slide showing images of three FOBT tests. The Guaiac FOBT costs $4.64, the FIT costs $22.22, and the Stool DNA tests cost $34-51, but $350-850 in practice

Credit: NCI

In a study conducted in 2007, researchers suggested that the FIT-type of FOBT had a higher ability for detecting left-sided colorectal cancer and that it might be a useful replacement for  guaiac FOBT.   Left-sided tumors tend to encircle the colon thusthey are more likely to obstruct the bowel. Higher sensitivities and specificities imply a greater accuracy for detecting colorectal cancer with FIT than with guaiac-based FOBT.

A technique called the Stool DNA test is another screening option for colorectal cancer. The lining of the colon continually sheds cells and these cells become bound up in the stool as it passes through the colon. Cells from the surface of precancerous polyps and cancerous tumors show recognizable DNA changes and a stool DNA test can identify several of these markers, indicating the presence of precancerous polyps or colon cancer.

In October 2008, a Mayo Clinic study published in the Annals of Internal Medicine found that  first-generation stool DNA tests were better than fecal blood tests for detecting cancer and precancerous polyps of the colon. In a follow-up study in January 2009, published in Gastroenterology, researchers showed technical improvements that nearly doubled the sensitivity of stool DNA testing for detecting premalignant polyps and increased cancer detection accuracy to about 90 percent. Researchers hope that the next generation tests will improve further in accuracy, processing speed, ease of patient use and affordability. However, a gold standard clinical trial comparing the effectiveness of the various tests is the only way to know for certain which test is the best at detecting colon cancer early. Currently, the United States Preventive Services Task Force (USPSTF) concludes that there is insufficient evidence to assess the benefits and harms of stool DNA testing as a screening modality for colorectal cancer.  The Task Force therefore does not recommend use of this test to screen average-risk adults for colorectal cancer.

Cost-effectiveness also is a factor when considering screening mechanisms.  Although not as costly as a colonoscopy , the Stool DNA test—costing $350 to $800—is far more expensive than the FOBT and is not covered by Medicare. At the NIH State-of-the-Science conference on Enhancing Use and Quality of Colorectal Cancer Screening, the independent panel recommended that financial barriers should be eliminated to assure that screening can be accessed by a larger population. Because of its ease of use and cost effectiveness, FOBT may have an important role in improving colorectal cancer screening rates and saving lives.

“Studies have shown that patient preferences for colorectal cancer screening tests vary, and many patients prefer FOBT over more invasive tests such as sigmoidoscopy and colonoscopy. Moreover, we have evidence from the Veterans Health Administration and Kaiser Permanente of Northern California that screening rates of 70 percent or higher can be achieved through programs that use FOBT as the primary colorectal cancer screening test,” said Carrie Klabunde, Ph.D., epidemiologist in NCI’s Division of Cancer Control and Population Sciences.

Print This Post Print This Post

Comments are closed.