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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Colonoscopy better than home test kit

Anthony L. Komaroff M.D.

DEAR DOCTOR K: I heard about a new home test that detects colon cancer. Is it a good alternative to colonoscopy?

DEAR READER: The new test appears to be an advance, but I don’t think it’s as good as colonoscopy.

Colon (or colorectal) cancer lies in the wall of the colon. It can cause painless bleeding. The amount of blood can be so small (“occult blood”) that it isn’t visible in the bowel movement, but it can be detected by chemical tests.

However, colonoscopy remains the best way for catching colorectal cancer early. This test, done under sedation, uses an instrument to look inside the colon. A similar procedure, flexible sigmoidoscopy, looks at about half of the colon and doesn’t require sedation. These tests not only can see cancer, but also abnormalities (adenomas) that can later become cancerous. The tests allow the adenomas and some very early cancers to be removed during the test.

In August 2014, the FDA approved Cologuard, a new test for colorectal cancer. The Cologuard test is done at home. You collect a stool sample and mail it to a laboratory for analysis. Like the fecal occult test, it checks for blood in stool. But the new test also looks for abnormal DNA.

One large study of nearly 10,000 people found the new test to be very effective. People in the study were given a fecal occult blood test, the Cologuard test and a colonoscopy. Cologuard detected 92 percent of the cancers that colonoscopy found; the fecal occult test detected 74 percent. Cologuard also found 69 percent of the polyps that were considered most likely to turn into cancer. The fecal occult test found 46 percent.

On the down side, the Cologuard test produced more false positives than the fecal occult test.

Cologuard offers another option for colorectal cancer screening. But right now, colonoscopy still remains the best screening method. It is recommended once every 10 years for people age 50 and over who have an average risk of colorectal cancer.