health

Doctors may use several methods to screen for colorectal cancer. The
simplest are a digital rectal examination (DRE) and a fecal occult blood
test (FOBT). In a DRE, the doctor inserts a gloved finger into the lower
part of the rectum to feel for tumors. The FOBT requires the patient to
take a kit home from the doctor’s office and collect a stool sample, which
is then returned to the doctor or a laboratory to be tested for occult
(hidden) blood. Patients must avoid eating rare meat and other foods
that can affect the test results before using the kit.

Other tests that may be used to diagnose colorectal cancer include:

• Blood tests for tumor markers, substances that can be analyzed to
  detect the presence of cancer.
  
• Barium enema. Barium in enema form is given to coat the lining
  of the colon and rectum. Air is then blown into the colon in order
  to fill it. The resultant x-ray can be used to detect precancerous
  polyps as well as cancerous tumors.
  
• Sigmoidoscopy. A sigmoidoscope is a flexible lighted tube that can
  be inserted into the rectum and used to examine the last 2 feet
  (0.6 meter) of the colon. It can be done in a doctor’s office but
  does not provide a view of the entire colon. If a polyp or tumor
  is found, the doctor will recommend a colonoscopy in order to
  check the upper part of the colon.
• Colonoscopy. A colonoscope is a long flexible tube attached to a
  video camera and monitor that allows the doctor to examine the
  entire length of the patient’s colon and rectum. The patient must
  take a laxative the night before to cleanse the bowel and may be
  given a sedative in the doctor’s office to make them more comfortable.
  The doctor can remove polyps during a colonoscopy or take
  tissue samples for analysis.
• Virtual colonoscopy. This technique uses computed tomography
  (a CT scan) to take images of the patient’s colon but is not yet
  available in all medical centers. Although virtual colonoscopy does
  not involve inserting a tube into the patient’s rectum, the patient
  must still take a laxative the night before to empty the bowel