How colon and rectal cancers are diagnosed

During a rectal examination, the doctor places a gloved finger into your back passage to feel for any lumps or swellings. This may be slightly uncomfortable, but it’s not painful. It will be less uncomfortable if you’re able to relax while you have the examination.

You may have a blood test to check for anaemia (a low number of red blood cells), which is common in people with bowel cancer. You may also have blood tests to check the health of your liver and kidneys.

If your GP is unsure what the problem is, or thinks that your symptoms could be caused by cancer, they will refer you to a hospital specialist. If your GP suspects you may have cancer, you should be seen at the hospital within 14 days.

At the hospital

At the hospital, the specialist will ask you about your general health, any previous medical problems, and whether you have any family history of bowel cancer. The specialist will examine you, and will probably repeat the rectal examination described on the opposite page.

One or more of the following tests may be used to diagnose bowel cancer:

Proctoscopy/sigmoidoscopy

These tests allow the doctor, or specialist nurse, to look at the inside lining of the rectum. They will usually be done in the hospital outpatient department.

A proctoscope is a short tube that goes just into the rectum.

A sigmoidoscope is a longer tube that can be passed further up into the large bowel. Any abnormal areas can be seen with the help of a tiny light and camera on the end of the tube.

If necessary, a small sample of the cells (a biopsy) can be taken for examination under a microscope. The biopsy will not be painful.

You’ll be asked to lie curled on your left side while a tube is gently passed into your back passage. You may be given an enema before the test, which will make you open your bowels. This makes the test more comfortable for you and easier for the person doing the test. During the test, a small amount of air is pumped into the bowel to make it easier to see inside it.

This will make you feel like you want to pass a bowel motion, but the feeling will gradually go away once the test is over.

A proctoscopy or a sigmoidoscopy can be uncomfortable but isn’t usually painful. You should be able to go home as soon as the test is over.

Colonoscopy

If your doctor wants to look inside the whole length of the large bowel, you may have a colonoscopy. This will usually be done in the hospital outpatient department and takes about an hour.

The bowel has to be completely empty for a colonoscopy.

This means following a careful diet for the day before your test. You’ll be given a medicine (laxative) to clear the bowel, usually on the day before the test. You will be given instructions by your hospital.

Just before the test, you may be given a sedative by injection into a vein (intravenously) to help you feel more relaxed. This may make you feel sleepy during the colonoscopy.

Once you’re lying comfortably on your side, the doctor or nurse will gently pass a flexible tube (a colonoscope) into your back passage. It can easily pass around curves and most of the large bowel can be examined. A tiny light and camera on the end of the tube help to show any abnormal areas or swelling.

During the test, photographs and samples (biopsies) of the cells on the inside of the large bowel can be taken.

A colonoscopy can be uncomfortable, but the sedative will help you feel more relaxed.

Most people are ready to go home a couple of hours after their test. You’ll need to arrange for someone to collect you from the hospital, as you shouldn’t drive for several hours after a sedative.

Virtual colonoscopy (CT colonography)

In this test, a CT scanner takes a series of x-ray pictures of your bowel. A computer then puts the pictures together to give a three-dimensional picture of your bowel.

A virtual colonoscopy is done in the hospital CT department, and you can usually have this test as an outpatient. It’s usually done as an alternative to a colonoscopy or if the large bowel could not be completely viewed during a colonoscopy.

Your bowel has to be completely empty for the scan, so you’ll need to follow a special diet for a few days and take a laxative before the test. Your hospital will give you instructions about how to prepare for it.

Your doctor may give you an injection of a medicine that will help the muscles of your bowel wall to relax. You may also have an injection of a dye (contrast medium) at the same time. Your doctor can let you know if you’re going to have this.

Just before the CT scans are taken, the doctor will pass a tube into your back passage (rectum) and pump in some air and gas (carbon dioxide). This expands the bowel and helps to give a clearer picture. You will have two CT scans - one while lying on your back and one while lying on your front. The computer then matches up the two scans to create a ‘virtual’ image of the inside of your bowel.