Screening Method Comparison

There are five main screening methods for colorectal cancer.  At our centers, we use the fecal occult blood test (FOBT), the only non-invasive method available.  It serves as an excellent initial screening due to its safe, simple and inexpensive nature.  For accurate results, hemorrhoids and anal fissures must be treated and resolved prior to FOBT screening to eliminate any known causes of blood in the stool.

Digital Rectal Exam

A digital rectal exam is often part of a routine physical examination.  During this brief procedure, a doctor or nurse inserts a lubricated, gloved finger into the rectum to feel for any abnormal growths.  If anything unusual is found, a more specific follow-up test is ordered.  A major limitation of this method is the inability to screen for growths in the colon, the five-foot long segment of intestine located above the rectum.   

Fecal Occult Blood Test (FOBT)

The FOBT screening involves gathering a small amount of stool at home so that it can be chemically tested for the presence of blood.  In many cases, blood in the stool may be the first, or only, warning sign of colorectal cancer as precancerous growths are known to bleed. Because other conditions may be responsible for blood in the stool, however, a colonoscopy is required after a positive FOBT to diagnose the cause of bleeding.

Colonoscopy

This precise but expensive diagnostic method involves inserting a long, flexible, lighted tube into the rectum and slowly guiding it into the colon.  Images are transmitted to a computer, and the physician looks for abnormal growths.  If any are found, the physician can surgically remove them for testing (called a biopsy).  To prepare for the 30-60 minute procedure, which is performed under sedation, patients must go on a liquid diet for one to three days and take a laxative or enema the night before. 

Sigmoidoscopy

Sigmoidoscopy is similar to colonoscopy, except that it only examines the rectum and lower third of the colon, called the sigmoid.  Thus, the test is shorter, around 10-20 minutes long, and more limited.  As with a colonoscopy, any abnormal growths that are discovered can be biopsied and sent for testing to determine if they’re cancerous.  At our centers, we use sigmoidoscopy for the evaluation of internal hemorrhoids. 

Double-contrast Barium Enema (DCBE)

DCBE is a series of x-rays of the lower intestine taken after the colon is filled with contrast material containing barium and inflated with air.  These measures allow for a detailed view of the lining of the colon, making the identification of growths easier.  Unlike a colonoscopy, however, abnormal growths cannot be removed during this approximately hour-long procedure, and a follow-up colonoscopy may be required.  This method also has a higher rate of missed lesions when compared to colonoscopy.

Virtual Colonoscopy

Virtual colonoscopy, also referred to as CT colonography, is a new form of x-ray used to detect polyps in which multiple dimensional images are taken to visualize the lining of the colon.  It is less invasive and less expensive than colonoscopy, has fewer risks and requires no anesthesia.  But small polyps may not show up, and if a polyp is found, a follow-up colonoscopy is needed.  Further studies are needed to determine the role of this new technique, which may not be covered yet by some insurance companies.

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