Diagnosis of Colorectal Polyps

In most cases, colorectal polyps are diagnosed during routine screening (e.g., rectal examination, laboratory tests, imaging tests). Physicians may be able to detect polyps in the lower rectum during a digital rectal examination (DRE). In this exam, the physician inserts a lubricated, gloved finger into the patient's rectum to feel for abnormalities.

The American Cancer Society recommends a yearly digital rectal exam beginning at the age of 40. DRE also may be performed prior to other screening tests, such as colonoscopy and sigmoidoscopy.

Laboratory Tests to Diagnose Colorectal Polyps

Fecal occult blood test (FOBT) can be used to detect hidden (occult) bleeding in the gastrointestinal (GI) tract. In this test, a chemical reaction is used to detect the presence of blood in a series of small stool samples. In many cases, the physician performs the initial test during a physical examination in the office, and then gives the patient a kit and further instructions for completing the test at home.

Results of the fecal occult blood test are not definitive, and the test detects blood in the stool in only about 5% of patients who have colorectal polyps. Certain foods (e.g., red meat, raw broccoli, cauliflower, turnips, melons), supplements (e.g., vitamin C), and medications (e.g., nonsteroidal anti-inflammatory drugs [NSAIDs]) can affect the results of this test.

A newer test, called the immunochemical fecal occult blood test (iFOBT), is more specific and produces fewer false results than standard FOBT. The iFOBT detects the presence of a certain protein (called globin) in the stool. Globin is found in a pigment called hemoglobin, which is an iron-containing substance in red blood cells.

Imaging Tests to Diagnose Colorectal Polyps

If blood in the stool is detected, an imaging test (e.g., colonoscopy, flexible sigmoidoscopy, double-contrast barium enema) often is performed to determine the source of the bleeding and the location of any colorectal polyps.

Imaging tests usually are performed in a hospital radiology department or in a physician's office. In most cases, patients are instructed to refrain from eating and drinking for a period of time (e.g., after midnight) prior to undergoing these tests. The day before, or the morning of the procedure, patients may be required to take a laxative and/or a cleansing enema to ensure that the colon is completely empty.

Colonoscopy, also called total colonoscopy, is the preferred test for diagnosing colorectal polyps. In this test, the physician examines the entire colon using a thin, hollow, lighted tube with a tiny video camera attached (called a colonoscope). The colonoscope is inserted into the rectum and passed through the colon, allowing the physician to examine the colorectal lining and detect polyps.

During colonoscopy, polyps can be removed using a cutting device or a wire loop (called a snare) through which mild electric current is passed. Removal of a polyp is called polypectomy. In some cases, a small sample of tissue is removed and examined under a microscope to determine if the polyp is cancerous (malignant). This procedure is called a biopsy.

In most cases, patients are given a sedative and pain reliever before undergoing colonoscopy. The procedure usually takes about 30 minutes to 1 hour to perform. Complications are rare and include bleeding and puncture of the colon.

Virtual colonoscopy is a less invasive test that can be used to detect colorectal polyps. During this procedure, air is introduced into the colon through the rectum and magnetic resonance imaging (MRI scan) or computed tomography (CT scan) are used to produce detailed images of the colon and rectum. Virtual colonoscopy takes about 20 to 30 minutes to perform.

Flexible sigmoidoscopy allows the physician to examine the rectum and lower part of the colon (i.e., sigmoid colon) and remove polyps. This procedure is similar to colonoscopy. The device used is called a sigmoidoscope. Flexible sigmoidoscopy usually takes about 20 minutes to perform. If a polyp is found during this procedure, a total colonoscopy usually is performed.

Double-contrast barium enema, also called barium enema with air contrast, is another imaging test that can be used to detect colorectal polyps. In this test, air and a contrast solution (barium) are introduced into the colon through a small tube inserted into the rectum. A device called a fluoroscope then is used to produce x-ray images of the colon and rectum. The contrast solution and air help provide clearer images and allow the physician to detect polyps in the colorectal lining easier.

Following these imaging tests, patients may experience side effects, including the following:

  • Abdominal pain or cramping
  • Bloating
  • Diarrhea
  • Nausea
  • Rectal irritation
  • Vomiting

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 28 Feb 2008

Last Modified: 08 Sep 2015