How to Detect Colon Cancer

Colon cancer is a common cause of cancer death in the United States and Western world. Current estimates place it as the second leading cause of cancer death. Sometimes referred to as colorectal cancer, up to one third of people diagnosed with colon cancer will die from it. Because of this very high mortality rate, extensive screening guidelines have been developed in an effort to detect colon cancer as early as possible. The earlier you can detect colon cancer, the more effective the treatments will be.

Aggressive screening for colon cancer allows for early detection of the disease, often before symptoms appear. In addition, some screening procedures can double as minor treatments. An example of this is the removal of benign polyps, some of which can eventually turn cancerous. Current guidelines recommend that all people begin screening for colon cancer at the age of 50. Up to 90% of all cases of colon cancer develop after age 50. In select high risk populations, screening procedures should begin as young as age 40.

Several factors go into making an effective screening test for detecting colon cancer. The test must have a high degree of sensitivity. This means that the test must be able to detect a majority of cases of potential colon cancer. A test which misses most many potential cancers is useless. In addition, the test must be specific. A test which gives a positive result in a wide range of different diseases is not as accurate or useful as a test which is positive for only colon cancer.

A good screening test must also entail as little risk to the patient as possible. Lastly, the screening test must also be able to detect the potential cancer at a very early stage, when something can still be done to effectively treat it.

Because most cases of colon cancer take many years to develop, early detection of a potential colon cancer can be quite effective in lowering a person’s risk of dying from this disease. Some colon cancer detection techniques have been shown to lower risk of developing colon cancer by up to 90%.

There are currently four major tests used to detect colon cancer. Each of these tests has advantages and disadvantages. This article is meant to be a quick introduction to each test. For more detailed information about each screening test, and its appropriateness to your health, you should speak with your doctor.

Fecal occult blood testing

The method used to detect colorectal cancer is fecal occult blood testing. Bleeding is a common symptom of colorectal cancer. Often this blood and can be hard to see by looking at your stool in the toilet. The fecal occult blood test is a way to detect very small amounts of blood in your stool which would otherwise be impossible to see.

The fecal occult blood test is relatively simple to administer. You are given a set of three credit card size, chemically treated paper cards. Each card has room for two small stool samples. Each stool sample is very small – a mere smudge on the paper. The cards are then folded up, sealed tightly, and sent to a lab for testing.

Fecal occult blood testing will give a very high number of false positive results. This means that only about 3-5% of positive results will actually lead to colon cancer in the future. This is because there are many possible causes of blood in the stool, not just colorectal cancer. If you have a positive fecal occult blood test, it does not mean you have, or ever will have, colon cancer. A positive fecal occult blood test will usually be followed up by your doctor with further testing.

Barium enema

A barium enema is another test used to detect colon cancer. The most commonly done version of this test is actually known as a double-contrast barium enema.

This test involves taking an x-ray of the entire colon and rectum. Before this is done, you will have a liquid solution containing barium injected in to your rectum. This liquid will cover the inside of your bowels. It is drained out before the x-ray is taken. The barium solution which coats the lining of the bowels shows up nicely on the x-ray, allowing the doctor to have a good look at the structures of your bowels.

A double-contrast barium enema is able to detect about 40 to 50% of precancerous polyps in the tested area. The test is a bit uncomfortable for the patient, but it is safe. Much like a fecal occult blood test, a barium enema which shows a potential cancerous area is usually followed up with a colonoscopy (discussed below).


A sigmoidoscopy is the first of two tests to detect colon cancer that allows a doctor to get a direct look of the inside of your bowels. The test involves the insertion of a small, flexible fiber-optic tube into the lower part of your colon. The test is often referred to by doctors as a “flex sig”.

There is a small camera on the end of the tube which is hooked to a TV monitor. This camera allows the doctor to take video and pictures of the inside of your bowels during the test.

A disadvantage of a flexible sigmoidoscopy is that it does not look at the entire large intestine. A doctor is only able to see about half of the total area of the colon and rectum. Flexible sigmoidoscopy involves little risk to the patient. In very rare cases, the camera can cause a small puncture or tear in the lining of the intestine.


A colonoscopy is a very similar test to a sigmoidoscopy. A major difference is that it is somewhat more invasive and allows the doctor to see the entire large intestine. In some cases, a colonoscopy will allow a doctor to remove small polyps. Some types of polyps can be pre-cancerous. Colonoscopy uses a similar camera to the flex sig, but it is a little larger and longer.

A colonoscopy can be somewhat uncomfortable for the patient. Because of this, a mild sedative is given to calm and relax the patient during the exam.

Colonoscopy has an excellent ability to detect many lesions which may be cancerous. The doctor is able to see the entire colon and rectum during this exam. There is some increased risk with a colonoscopy compared with some of the other tests used to detect colon cancer. The tube used to do the exam can puncture the wall of the bowel, although this is still quite a slim possibility.

You should work with your doctor to develop a screening plan and assess your risk for colon cancer. Each of these tests are important in the process of early detection for colon cancer, however you must work with your doctor to determine which of them may be most appropriate for you. If you have specific questions about the details of any of these exams, speak with your doctor.