Unlike many kinds of cancer, colorectal cancer can be found in early stages. Early diagnosis usually results in better chances for curing the disease. Screening tests for colorectal cancer include:

• Fecal occult blood test (FOBT). This test checks for blood in stool samples. Patients receive a kit that can be completed in a doctor’s office or with instructions to be completed at home. Dietary restrictions may include avoiding red meat, vitamin C, aspirin and aspirin substitutes for several days before testing. Patients return the kit to their physician’s office or a medical lab for analysis. Some home kits provide immediate results through the use of chemically treated papers. These strips of paper can detect the presence of occult blood. Typically, three bowel movements are tested and the results are recorded by the patient. The results are then mailed back to the physician’s office.
  
  Annual FOBT can reduce deaths from colorectal cancer by 33 percent and incidence of colorectal cancer by 20 percent, according to the U.S.  Centers for Disease Control and Prevention (CDC). Colorectal cancer does not always cause bleeding, and this test can therefore give false negatives (indicating no cancer when cancer is present).
  
  
• Fecal immunochemical test (FIT). This test works similar to the FOBT but is a more specific assessment of a blood protein, which can reduce the number of false negatives. It is easier to use because it does not involve dietary restrictions and usually requires two stool samples rather than three. However, like FOBT it does not reveal tumors that do not bleed.
  
  
• Flexible sigmoidoscopy. The physician inspects the interior of the rectum and the lower colon (the sigmoid) with a flexible, lighted tube called a sigmoidoscope. Deaths from cancer of the rectum and sigmoid colon are more than 50 percent lower among people who have had sigmoidoscopy, according to the CDC.
  
  
• Colonoscopy. A longer flexible, lighted tube with a camera lens called a colonoscope that allows a physician to inspect the rectum and entire colon. The device is connected to a video camera and monitor. The physician may pass a wire through the colonoscope to remove polyps with an electric current. Tissue samples can be taken for microscopic examination in a biopsy.
  
  
• Double-contrast barium enema. X-rays are taken after a chemical compound containing barium is administered into the patient’s rectum through a tube. Air is also pumped into the rectum to enlarge the bowel. The barium outlines the colon and rectum on the x-ray image and helps reveal abnormalities, such as polyps. 

A newer procedure that might be an option is virtual colonoscopy (colonography or CT colonography). This test uses a CAT scan to take pictures of the colon. A CAT scan creates cross-sectional images than can reveal polyps or other irregularities. However, virtual colonoscopy is not as accurate as colonoscopy and is not as widely available. The ACS does not recommend it for early diagnosis of colorectal cancer until more research confirms its effectiveness.

In some men, a digital rectal exam (DRE) is part of a physical examination. The physician carefully inserts a gloved, lubricated finger several inches into the rectum to feel for abnormalities. However, the CDC and ACS advise against screening for colorectal cancer with only the DRE because it involves only a small part of the colorectal tract.

Other tests that may be used in diagnosing or treating colorectal cancer:

• Blood tests. Includes complete blood count and tumor marker tests (substances tumors release into the blood).
  
  
• Ultrasound. Use of harmless sound waves that create echoes to form a picture of the colon or rectum.
  
  
• Magnetic resonance imaging (MRI).  Use of radio waves and a magnetic field to create a picture of the colon or rectum.

• Computed tomography (CT or CAT scan). A type of x-ray that produces cross-sectional images of the body. A contrast dye may be injected into a patient’s vein to help highlight the inner structures. A type of CAT scan that may be used with metastatic colorectal cancer is spiral CT, in which the injected dye travels to the liver to reveal if cancer has spread to this organ.
  
  
• Angiography. A type of x-ray that reveals abnormalities in blood vessels. A contrast dye is injected into a vein or an artery. This test may be used to help surgeons identify blood vessels feeding a cancer that has spread to the liver. The test can help with surgical treatment of the cancer.
  
  
• Positron emission tomography (PET). Use of a radiation-detecting PET machine to scan the entire body for cancer. A small amount of a radioactive sugar substance is injected into the patient before a series of images are taken. Cancer cells absorb large amounts of this radioactivity and show up on the scan as “hot spots.” A PET scan is often used to help determine if and where cancer has spread in the body. Technology that combines PET and CT scanning is also being used for more accurate staging and treatment of colorectal cancer.

The ACS recommends that both men and women at average risk should complete ONE of the following screening options:

• FOBT (or FIT) every year
• Flexible sigmoidoscopy every five years
• Blood stool test every year plus flexible sigmoidoscopy every five years
• Double barium contrast enema every five years
• Colonoscopy every 10 years
  

People at higher risk of colorectal cancers should start screening at a younger age and may need testing more often, according to the CDC. The American Cancer Society (ACS) recommends that people with familial adenomatous polyposis begin colonoscopy during their teens.