Screening tests, conducted prior to the onset of symptoms, are recommended for individuals at the age of 50 years and above to detect precancerous polyps. This allows the polyps to be removed before they develop into cancer or detect colorectal cancer at its early stages, when treatment is more likely to be effective.
Once symptoms appear, diagnostic tests are recommended to allow doctors to confirm if it is colorectal cancer, assess the stage and determine the best course of treatment.
These tests are commonly used to diagnose colorectal cancer:
Faecal occult blood test or blood stool test
Faecal occult blood test or blood stool test checks for the presence of blood in stools (faeces). However, as several conditions could cause the presence of blood in stools, a positive result may not be sufficient to confirmation a diagnosis of colorectal cancer.
Sigmoidoscopy uses a flexible, slender tube with a light inserted into the rectum and sigmoid (the part of the colon just before the rectum) to detect polyps or colon cancer in the end-third of the colon and rectum. If either are detected, a colonoscopy may be recommended.
Colonoscopy is similar to a sigmoidoscopy but with longer tube and with an attached video camera and monitor, allowing the doctor to view the entire length of the colon and rectum. This procedure also allows the doctor to remove any polyps, or take tissue samples for further testing.
Barium enema is an imaging test that uses barium (contrast dye) and x-ray to create a clear image of the colon and rectum, allowing the doctor to detect signs of colorectal cancer. In a double-contrast barium enema, air is added to expand the colon and provide a more detailed view of the inner lining of the colon.
CT colonography or virtual colonoscopy, uses low dose radiation CT scanning or magnetic resonance imaging to obtain an interior view of the colon (the large intestine) and rectum (back passage) that are otherwise only seen with a more invasive procedure where an endoscope is inserted into the rectum and passed through the entire colon.