Screening tests for colorectal cancer

Colorectal cancer is the second-leading cause of cancer deaths. The good news is: It’s also one of the most preventable cancers, thanks to advanced screening options.

The two main screening tests for colorectal cancer are 1) stool-based screening, and 2) colonoscopy.

What is stool-based screening?

In stool-based screening tests, patients collect a stool sample at home using a kit. The kit usually includes a mailing envelope or box in which to send the sample to a medical lab for testing. There are two main types of stool-based tests:

Stool DNA test: You may have seen this type advertised on TV. It tests for DNA mutations from colorectal cancer or polyp cells which make their way into the stool. It also tests for blood in the stool, another symptom of colorectal cancer.

Fecal Immunochemical Test (FIT) or Guaiac-based Fecal Occult Blood Test (gFOBT): Both of these tests screen the stool for blood, just using different methods.

Pros and cons of stool-based testing:

Pros: These tests are easier for the patient, are not invasive and do not require a visit to the hospital.

Cons: They must be performed more frequently than other tests — every year for FIT and gFOBT, every three years for Stool DNA). Also, if the tests find blood or DNA changes, a colonoscopy must be performed.

What is a colonoscopy, and who needs it?

A colonoscopy is a screening procedure in which a long tube (colonoscope) with a tiny camera at the end is inserted into the colon through the rectum. Through this scope, the doctor can view the inside of your entire colon to check for any abnormalities. A colonoscopy is recommended for:

  • Patients 50-75 years of age (patients 76-85 should consult with their physician to see if screening is recommended; screening is not recommended for those over the age of 85)
  • Patients with a family history of colorectal cancer or certain types of polyps
  • Patients with a personal history of colorectal cancer or certain types of polyps
  • Patients with a personal history of inflammatory bowel disease
  • Patients with a personal history of radiation to the abdomen or pelvic area for prior cancer

Your doctor may also prescribe a colonoscopy if you have a positive stool-based test (see above), are experiencing abdominal pain, rectal bleeding, chronic constipation or diarrhea, or have other intestinal problems.

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The colonoscopy itself is a short procedure (30-60 minutes). The prep for a colonoscopy takes a bit longer.

Colonoscopy prep: What to expect

The goal of colonoscopy preparation is to completely empty your colon. You’ll do this at home. You can help the cleansing process by eating lightly the 3-4 days before and eating low-fiber, easily digestible foods. If you take regular medications, ask your doctor if you should continue taking them in the days before your procedure.

Prep methods vary, but usually will include:

  • A day without solid food. Clear liquids like water, broth, and tea are allowed.
  • You’ll drink a laxative solution your doctor will prescribe. The laxative will induce diarrhea.

The colonoscopy procedure

Most colonoscopies are performed while the patient is under sedation. An IV will be inserted in your arm or hand, and medication will be delivered through the IV. Afterward, you may experience some gas pains from air inserted into your colon during the colonoscopy (this helps the doctor view the inside of the colon).

You must have someone accompany you to the colonoscopy location and stay for the duration of the procedure. You can go home shortly after the procedure, but since you will still be groggy from the sedation, you will need someone to drive you home.

The results

If the doctor finds no polyps or abnormal tissue, and you have no other risk factors for colorectal cancer, you probably won’t need another colonoscopy for ten years.

If the doctor finds any polyps, he or she will likely remove them during the colonoscopy. Polyps removed during a colonoscopy will be sent to a laboratory for analysis to determine if they are cancerous, precancerous, or noncancerous.

Depending on the results, you may need to have more frequent colonoscopies to monitor your condition.