Diagnosis of Colon Polyps

How does a doctor diagnose colon polyps?

Your doctor can only find colon polyps by using certain tests or procedures. Your doctor may also find polyps while testing you for other problems.

Medical and family history

Taking a medical and family history may help a doctor determine which test is best for you.

Doctor taking a patient's medical history

Physical exam

After taking a medical and family history, your doctor will perform a physical exam to help determine what testing is best for you.

Stool test

A stool test is the analysis of a sample stool.

Your doctor will give you a test kit and instructions for taking a sample at home. For some tests, you may need to change your diet for a few days before the test. You will receive instructions on where to send or take the kit for analysis.

Flexible sigmoidoscopy

Flexible sigmoidoscopy is a procedure that uses a flexible, narrow tube with a light and tiny camera (called a sigmoidoscope) on one end to look inside your rectum and lower colon.

The procedure can show irritated or swollen tissue, ulcers, and polyps. During the procedure, the doctor can take a biopsy. You won’t feel the biopsy.


Colonoscopy is a procedure that uses a long, flexible, narrow tube with a light and tiny camera on one end to look inside your rectum and colon (called a colonoscope).

Colonoscopy can show irritated or swollen tissue, ulcers, polyps, and cancer. A trained specialist performs this procedure. The colonoscope has a tool that can remove polyps. A trained specialist typically removes polyps that he or she finds during colonoscopy. A pathologist will check the polyps for cancer.

A patient lying on their side while a doctor performs a colonoscopy and a depiction of the lower GI tract examined during a colonoscopy (including the colon, rectum, colonscope, and anus).
Colonoscopy testing

Virtual colonoscopy

Virtual colonoscopy uses computerized tomography (CT) to look inside your rectum and colon. CT machines use a combination of x-rays and computer technology to create images. Virtual colonoscopy can show irritated or swollen tissue, ulcers, and polyps. Doctors can’t remove polyps during virtual colonoscopy. If virtual colonoscopy shows a polyp, doctors will most often recommend a colonoscopy to confirm the diagnosis and remove the polyp.

Lower gastrointestinal (GI) series

A lower GI series is an x-ray that doctors use to look at your large intestine. For the procedure, you’ll be asked to lie on a table while a health care professional inserts a flexible tube into your anus. Next, the health care professional fills your large intestine with barium, which makes polyps show up more clearly on x-rays. Doctors most often use lower GI series in combination with flexible sigmoidoscopy, because flexible sigmoidoscopy doesn’t examine the entire colon.

November 2014

This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.