The first step in diagnosis is usually an examination of your rectum by a doctor. You may also be asked to take a stool sample to your doctor so it can be tested for blood. If your doctor thinks that cancer may be present, or is unable to provide a diagnosis, they will refer you to a specialist. The following tests are all used in the diagnosis of colorectal cancer.

Initial screening

• Digital rectal examination

  This is usually the first check for colorectal cancer. It involves a doctor gently inserting a gloved finger into the rectum to check for any lumps or swellings.

• Faecal Occult Blood Test (FOBT)

  This is a test to detect the presence of human blood in a single stool sample. If the result is positive, a colonoscopy should be arranged for further examination. Currently, the Government’s Colorectal Cancer Screening Programme subsidises screening for asymptomatic Hong Kong residents aged 50 to 75 in the private sector for colorectal cancer. The first screening test is the faecal occult blood test, and if the result is positive, a colonoscopy will be arranged. For more details, please visit the webpage for "The Department of Health's Colorectal Cancer Screening Programme".

• Faecal Immunochemical Test–DNA (FIT-DNA)

  A FIT-DNA test checks for blood and genetic mutations in the stool to assess the risk of colorectal cancer. The detection rate for colorectal cancer is about 90%, but its sensitivity for important polyps (which could develop into cancer) is relatively lower. If the result is positive, a colonoscopy is needed for further examination.

• Colonoscopy

  In this procedure, a doctor or nurse will gently pass a flexible tube (a colonoscope) into your back passage. The tube is flexible and can be used to examine the entire length of the large bowel.

• Virtual colonoscopy

  A virtual colonoscopy is a non-invasive examination that uses computer scanning technology to create images of the colon, allowing for the detection of polyps or tumours within the colon. If polyps or tumours are found, a colonoscopy should be performed to remove the polyps or to obtain tumour tissue for pathological testing.

• Cancer index

  A cancer index, also known as “tumour markers,” refers to the concentration of certain proteins or substances related to cancer cells that can be measured in the blood. By tracking changes in these values, doctors can monitor the development and progression of some cancers. There are many types of tumour markers. For colorectal cancer, the main marker is carcinoembryonic antigen (CEA), with a normal value being less than 5 ng/ml. CEA can be checked with a blood test, even during a routine health check-up. However, CEA is not used to diagnose colorectal cancer, since high levels can be a result of many causes, such as long-term smoking, inflammatory bowel disease, liver cirrhosis, or hypothyroidism. Instead, CEA is mainly used to monitor for recurrence and to assess treatment effectiveness in colorectal cancer patients.

Further tests

If tests indicate that you have colorectal cancer, your doctor may wish to conduct further tests to see if the disease has spread. The results will help your doctor decide the best type of treatment.

• Liver function test

  This blood test measures chemicals that are normally found or produced in your liver. An abnormal result can indicate that cancer has spread to the liver.

• X-ray

  This is used to test if colorectal cancer has spread to the lungs.

• Ultrasound scan

  High-frequency sound waves are used to create images of the abdomen and liver. The doctor will apply a thin layer of gel to your abdomen and then move a small probe over the area. The whole process only takes a few minutes, it is painless, and has no lingering effects.

• Computerised Tomography (CT scan) and Magnetic Resonance Imaging (MRI) scan

  CT scan and MRI are both non-invasive methods used to check whether cancer cells have spread to or invaded nearby tissues and other organs. Although the imaging principles of the two are similar, MRI uses magnetic fields instead of X-rays to create cross-sectional images of the body.

  During the MRI scan, you’ll need to lie still inside a large tube that’s open at both ends. The whole process takes about 30 minutes. The machine makes loud noises, so medical staff usually provide earplugs.

You may need to wait a few days for the results of these tests. During this time, you might feel anxious—talking to family or friends can help ease your emotions.