Bleeding in the digestive tract can lead to blood in the stool. In fact, having occasional small traces of blood in the stool is not abnormal. Faecal blood in amounts greater than normal, but not noticeable visually, is called occult blood. The occult blood test detects digestive tract bleeding in the stool and is used to screen for colon and rectal cancer.
Colon cancer is a major cause of death in the western world. One of the early clues to colon cancer is occult bleeding in the bowel movement. For this reason, regular occult blood testing can be life-saving. Doctors recommend regular occult blood tests starting at age 50.
Before the test, the patient should eat a high fibre diet for 2 or 3 days. Certain raw foods, turnips, horseradish, and red meat should be avoided. Testing may take place in a lab or clinic. Doctors may also give the person a kit to collect samples at home.
Three or more stool specimens are collected. The test involves mixing a small sample of stool with a chemical that reacts with blood. If there are normal amounts of blood, the reaction is green. If there is occult blood, the test turns dark blue within 5 minutes. A common home kit contains a folder that has 3 panels containing the chemical. It also provides 3 flat sticks for applying the samples to the panels. The person seals the folder and mails it to a medical lab. Lab technicians process the panels and observe the reaction.
Reasons for digestive tract bleeding include haemorrhoids, leaking blood vessels, ulcers, ulcerative colitis, dysentery, or simply an unusual diet. A positive test result may also indicate polyps in the colon or rectum. Polyps are not cancer, but they can become cancer.
Further tests are necessary to define the cause. These may include:
- endoscopy, when a flexible scope is used to examine the intestines
- a barium swallow, or a barium enema, where x-rays are taken after contrast material is swallowed by mouth or given by enema.
