Understanding Colorectal Cancer: The Diagnosis

If you are being examined for colorectal cancer, the first thing your doctor will do is review your medical history. He or she will conduct a thorough medical exam. Your doctor may conduct one or more of the following tests.

Physical Exam

Digital Rectal Exam

Why it is done: This is to check the rectum for lumps or abnormalities. About half of rectal cancers can be detected in this way.

What to expect: The doctor will insert a lubricated, gloved finger into the rectum. A rectal exam is particularly helpful if a test for occult (hidden) blood is conducted at the same time.

Stool Tests

Fecal Occult Blood Test

Why it is done: Blood in stool (bowel movement) can indicate colorectal cancer. It’s sometimes hidden, or not visible to the naked eye. Stool may contain blood for many reasons. It does not always mean colorectal cancer.

What to expect: In this procedure, a small sample of stool is placed on a chemically treated card. A laboratory then tests it for hidden blood. If there is blood found in the stool sample, a more specialized test like colonoscopy may be necessary. Your doctor should give you special instructions on which foods and medications to avoid before the test to decrease false results.

Fecal Immunochemical Test (FIT)

Why it is done: It detects blood in stool just like the fecal occult blood test, but this tests looks for it in a different way. It tests the stool for blood by seeing how it reacts to a special protein found in blood.

What to expect: The collection process is similar to the fecal occult blood test but you do not have to avoid food or medications. If the test results are positive you may need to have a colonoscopy for further evaluation.

Stool DNA Test

Why it is done: To detect cell changes in the stool that could indicate colon cancer or pre-cancerous polyps.

What to expect: You’ll get a kit in the mail to collect a stool sample. The kit will come with instructions, supplies and a shipping box. Not all insurance plans will pay for this test. If the result is positive you will need a colonoscopy for further evaluation.

Imaging Tests

The following imaging tests will require you to take medications and/or enemas to clean your bowel out for the procedure.

Barium Enema

Why it is done: An X-ray provides a picture of the colon. This helps the doctor identify polyps and abnormalities.

What to expect: This is done by instilling barium, a thick white liquid, and air into the colon through a rectal tube. This is an uncomfortable procedure, but not painful. It takes about an hour. The barium coats the intestine and provides contrast so polyps show up better on the X-ray. This test does not capture all polyps and is not as effective as a screening tool.

Virtual Colonoscopy

Why it is done: This is a type of CT scan. It uses computer software along with CT imaging to examine the colon for polyps.

What to expect: In this procedure, a rubber catheter is inserted to force air into the colon. Some of the benefits of a virtual colonoscopy are that it:

  • Does not require the insertion of tubes (as in colonoscopy).
  • Prevents the slight risk of possible injury to the bowel.
  • Does not require sedation.
  • Makes recovery time shorter.
  • Means the person having the procedure won’t need someone to drive them. 

Virtual colonoscopy is not available everywhere. Some doctors feel it is almost as effective as endoscopy in identifying polyps. However, if a polyp is found by virtual colonoscopy, a second procedure will be needed to remove and examine it. With conventional colonoscopy, the biopsy can usually be done at the same time.

Endoscopic Tests

The following endoscopic tests will require you to take medications and/or enemas to clean your bowel out for the procedure.

Colonoscopy

Why it is done: Colonoscopy is used to examine the bowel’s interior surface for abnormalities like polyps.

What to expect: You will be sedated for this procedure. The doctor inserts a flexible tube into the bowel. The tube contains a camera. The colonoscopy lets the doctor examine the inside of the entire colon and rectum. If the doctor discovers a polyp or abnormal tissue, it may be removed and sent for further testing. Removal of a polyp is called polypectomy. Colonoscopy is considered to be the gold standard screening test by many doctors because the doctor is able to look at the entire colon, take biopsies if needed, remove polyps and mark suspicious sites with ink for surgery.

Flexible Sigmoidoscopy

Why it is done: A flexible sigmoidoscopy (flex sig), like the colonoscopy, is used to examine the bowel’s interior surface for abnormalities like polyps.

What to expect: In this procedure, the doctor inserts a flexible tube inside into the bowel. Air is instilled through the tube to allow the colon to expand. The flex sig lets the doctor examine the inside of the sigmoid (lower) colon and rectum. If the doctor discovers a polyp or abnormal tissue, it may be removed and sent for further testing. This test takes approximately 10-15 minutes and only looks at a portion of the colon. Sedation is generally not given.

Biopsy

Biopsy

Why it is done: A biopsy allows the doctor to remove a tissue sample to then be sent to a pathologist for examination under the microscope.

What to expect: A biopsy can be done during endoscopic procedures. In these procedures, the doctor uses a special instrument placed through the scope to take samples of growths and abnormalities along the lining of the colon and rectum.

Next: How is colorectal cancer staged?

Back to “Understanding Colorectal Cancer: An Introduction”