Diagnosis of Colorectal Cancer

Diagnosis involves screening to detect colorectal cancer in asymptomatic patients (i.e., those without symptoms) with no family history of the disease.

Screening is recommended for most average-risk patients beginning at age 50, and for African-American patients beginning at age 45. Screening includes the following:

  • Digital rectal examination (DRE) and fecal occult blood test annually and
  • Double-contrast barium enema every 5–10 years and
  • Flexible sigmoidoscopy every 5 years, or
  • Total colonoscopy every 10 years

Diagnosis of colorectal cancer in symptomatic patients and high-risk patients includes laboratory and imaging tests. Biopsy (i.e., removal of a tissue sample for examination under a microscope) is necessary to confirm the diagnosis.

In digital rectal examination (DRE), the physician inserts a lubricated, gloved finger into the patient's rectum to feel for tumors. Approximately 5–10 percent of colorectal cancers are palpable (i.e., able to be felt).

Fecal occult blood test is used to detect microscopic blood in the stool, which may indicate early colorectal cancer. When results of this test are positive, the diagnosis is confirmed using additional procedures (e.g., barium enema, sigmoidoscopy, colonoscopy).

When colorectal cancer is suspected, laboratory tests such as urinalysis, blood tests (e.g., carcinoembryonic antigen level, complete blood count, electrolyte and chemical panels), and imaging tests are performed.

In August 2014, the U.S. Food and Drug Administration (FDA) approved the stool test Cologuard, which detects the presence of red blood cells in the stool and DNA mutations that may indicate colorectal cancer and abnormal growths that may progress into colorectal cancer. The approval of this diagnostic test does not change the screening guidelines outlined above.

Updated by Remedy Health Media

Publication Review By: Toomas Sorra, M.D., F.A.C.G.

Published: 14 Aug 1999

Last Modified: 22 Jul 2015