Stool DNA testing was added to the colorectal cancer screening recommendations in March of 2008. However, the test is recommended primarily for the detection of cancer, not polyps or precancerous lesions.
Cells that line the lower intestinal tract are constantly being shed into the colon, picked up by feces, and excreted in bowel movements. When normal cells change into precancerous or cancerous ones, their DNA changes or mutates. By looking at markers for genes that are commonly changed in cancers and precancerous polyps, DNA stool tests can identify patients who need further colonoscopy testing.
To complete a DNA stool test, the patient obtains a specimen kit to collect one entire bowel movement which is then mailed back to the testing laboratory in a special container with an ice pack. There is no need to handle stool. No bowel preparation or special diets are necessary before the sample is obtained, and only one stool sample needs to be collected.
Results are available in about three to six weeks. If the test is positive, follow-up colonoscopy is necessary to evaluate lesions and remove any polyps. The right time between screening tests with stool DNA is still uncertain.
There is currently a DNA stool test available commercially, PreGen-Plus™ (Version 1.1) that looks at markers for 23 genes commonly changed in adenomas and cancer. While it is more sensitive than fecal occult blood testing, it is not as sensitive as colonoscopy and will miss about half of cancers in a average risk group of people without symptoms.
Research is underway to improve the sensitivity of DNA stool tests by looking at additional markers and reducing DNA degradation during transportation and handling time.
Where Can You Go for More Information
More information about the PreGen-Plus™ test, including a short video, is available from DNADirect, a commercial genetics testing laboratory. (C3 does not endorse any particular laboratory for testing.)
Fecal DNA vs Fecal Occult Blood Testing for Colorectal Cancer Screening in an Average Risk Population in The New England Journal of Medicine, December 23, 2004, lead author Thomas F. Imperiale MD reports on research comparing fecal occult blood testing to DNA stool testing.