Houston Methodist. Leading Medicine.
Houston Methodist. Leading Medicine

Colon & Rectal Cancer Screening

Screening for Colon and Rectal Cancer
Screening for colon and rectal cancer can detect precancerous polyps, which can be present in the colon for up to 10 years before invasive cancer develops. The Center for Disease Control reports that when colon cancer is found early through screening and treated promptly, the 5-year relative survival rate is 90 percent.

Risk Factors for Colon Cancer
Digital Rectal Exam
Fecal Occult Blood Test (FOBT)
Virtual Colonoscopy (Computerized Tomographic Colonography)
Double Contrast Barium Enema (DCBE)

Risk Factors for Colon and Rectal Cancer
The screenings your doctor recommends will depend heavily on your risk factors for developing colon and rectal cancer. Keep in mind that having one or more risk factors does not mean you will definitely get the disease, and having no risk factors does not mean you cannot get it.

Studies have linked several factors to the risk for colon cancer:

  • Being age 50 or older
  • Personal or family history of colon cancer
  • History of bowel disease
  • A diet high in red meats
  • Lack of exercise
  • Being overweight
  • Smoking
  • Alcohol use (more than 1–2 drinks a day)
  • Type 2 diabetes

It’s important that both you and your doctor are aware of any factors that could increase your risk of developing colon cancer.

Digital Rectal Exam
A digital rectal exam is often part of a routine physical examination. Your doctor inserts a lubricated, gloved finger into your rectum to feel for abnormalities. If he or she finds anything unusual, additional screening tests may be performed.


Fecal Occult Blood Test (FOBT)
A fecal occult blood test (FOBT) checks for blood in the stool that you may not be able to see.

For this test, your doctor will ask you to submit a sample of your stool so that it can be examined by the lab. How the sample is collected depends on the specific type of FOBT your doctor wants the lab to perform, so make sure to get specific instructions before you leave the office.

Currently, two types of FOBT are available:

  • Guaiac FOBT uses the chemical guaiac to detect heme (the iron-containing component of the blood protein hemoglobin) in samples of stool.
  • Immunochemical (or immunohistochemical) FOBT uses antibodies to detect the blood protein hemoglobin in samples of stool.

In a sigmoidoscopy, your doctor inserts a flexible, lighted instrument called a sigmoidoscope into your rectum and lower colon to look for signs of polyps or cancerous tissue.

When you schedule your exam, you’ll be given instructions on how to prepare for it. This usually includes using an enema to empty your bowels about one hour before the sigmoidoscopy. On the morning of the procedure, you’ll want to eat a light breakfast.

  • You will be asked to lie down on a table, on your left side with your knees drawn up toward your chest.
  • First, the doctor will gently insert a gloved, lubricated finger into your rectum to check for blockage and to enlarge the anus.
  • The sigmoidoscope is inserted through the anus and gently moved into your colon. At the same time, air is gently pumped in to open up the area and help your doctor see better.
  • If your doctor wants to take tissue samples, he or she may pass a tiny biopsy tool through the scope. If polyps are found, another tool may be used to remove them with heat (electrocautery).


The test usually takes 10–20 minutes; while you may experience some discomfort, this is usually temporary.


A colonoscopy is similar to a sigmoidoscopy, except that a sigmoidoscopy only lets your doctor see the lower (descending) colon, while a colonoscopy lets him or her examine the entire colon. Like in a sigmoidoscopy, your doctor can pass very small tools through the colonoscope to take cells for a biopsy or to burn off polyps.

Preparing for your colonoscopy will take 1–2 days, depending on the type of prep recommended to you. The goal of the prep is to make sure your colon is empty for the test, so you’ll need to forego solid foods and take a solution that triggers bowel-clearing activity. During your prep days, you’ll want to stay home since you will need to use the bathroom often. Since you’ll be sedated for the test, you’ll want to have someone drive you to and from the hospital or clinic on the day of the procedure.

Because a colonoscopy goes deeper into the colon, you may be given pain medication and a sedative before the procedure to help you relax. You may feel sleepy during the test and may not remember much afterwards.

After the exam, you will stay in the hospital or clinic for 1–2 hours until the sedative wears off. You may receive the results before you leave, or your doctor may schedule a follow-up appointment.

Most people have no problems after a colonoscopy, but you should contact your physician if you notice heavy bleeding from your anus, abdominal swelling or pain, or if you feel sick or have a fever.


Virtual Colonoscopy (Computerized Tomographic Colonography)
A virtual colonoscopy uses computerized tomography (CT) to take multiple images of your abdominal organs. A computer is then used to assemble these images into a detailed view of the colon and rectum. Because it’s less invasive than a traditional colonoscopy, it usually requires no sedation, and it only takes about 10 minutes.

  • If necessary, a contrast dye may be injected before the test to help create clearer images.
  • You’ll lie on your side on an examination table with your knees drawn up to your chest.
  • The doctor will place a small tube (catheter) inside your rectum to fill your colon with air, which helps create clear images. This may cause a feeling of pressure in your abdomen.
  • You’ll then be asked to lie flat on your back and the exam table will be moved into a CT machine, where your body will be scanned.
  • You may be asked to turn over and hold your breath at times while the images are taken.


After the exam, most of the air will be removed from your colon through the catheter, and you may feel bloated or pass gas for a few hours afterward until the rest of the air is cleared. Walking may help relieve any discomfort, and you can return to your usual diet and activities right away. Consult your doctor if your symptoms don't improve on their own.


Double Contrast Barium Enema (DCBE)
A double contrast barium enema (DCBE) uses X-rays and a contrast material called barium sulfate to check for abnormal areas in the colon.

As with a colonoscopy, your colon will need to be empty for the DCBE to be effective. Your physician will give you specific instructions on preparing for the test, which may involve taking laxatives and/or taking an enema the morning of the exam. You will also be asked to follow a clear liquid diet for 1–2 days before the procedure.

  • You’ll lie on a table on your side in an X-ray room.
  • A small, flexible tube is inserted into your rectum, and barium sulfate is pumped in to partially fill and open up your colon.
  • When your colon is about half-full of barium, you will be asked to turn flat on your back so the barium spreads throughout the colon.
  • Air is pumped into the colon through the same tube to make it expand. This may cause some cramping and discomfort, and you may feel the urge to have a bowel movement.
  • The technician then takes X-ray images of the lining of your colon; you may be asked to change positions and occasionally hold your breath so that different views of the colon and rectum can be seen on the X-rays.


If polyps or other suspicious areas are seen on this test, a colonoscopy will likely be needed to remove them or to explore them fully.

To learn more about colon cancer screening at the Methodist Cancer Center, please call us at 713-790-2700.

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