How colon and rectal cancers are diagnosed

Usually, you begin by seeing your GP (family doctor). They will examine you and may refer you to hospital for tests.

Seeing your GP Back to top

Your GP will feel your abdomen and examine your back passage (a rectal examination). To do this, the doctor places a gloved finger into your back passage to feel for any lumps or swellings. This may be slightly uncomfortable but it is not painful. It will be less uncomfortable if you are able to relax while they are doing this.

You may have a blood test to check for anaemia (a low number of red blood cells), which is common in people with cancer of the colon or rectum. 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.

At the hospital Back to top

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 (as above).

The following tests may be used to diagnose colon and rectal cancer:

• proctoscopy or sigmoidoscopy – to look at the inside lining of the rectum or sigmoid colon
• colonoscopy – to look inside the whole length of the large bowel
• barium enema – a special x-ray of the colon and rectum
• CT colonography – a scan that is sometimes done instead of a barium enema

How the tests are carried out Back to top

Proctoscopy/sigmoidoscopy

These tests are done in the hospital outpatient department or on the ward by a doctor or nurse colonoscopist.

You will be asked to lie curled on your left side while a tube is gently passed into your back passage. A small hand-pump is attached to the tube so that air can be pumped into the bowel. This makes you feel that you want to pass a bowel motion, but the feeling will gradually go away once the test is over.

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 is not painful.

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.

For a colonoscopy the bowel has to be completely empty. This means following a careful diet for a few days before your test. The preparation is similar to that for a barium enema (see below). You will be given instructions by your hospital.

Just before the test, you may be given a sedative tablet to help you feel more relaxed, and you may feel sleepy during the colonoscopy. Once you are lying comfortably on your side, the doctor or nurse will gently pass a flexible tube (a colonoscope) into your back passage. The tube is made up of flexible fibres. 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. It’s a good idea to arrange for someone to collect you from the hospital, as you shouldn’t drive for several hours after a sedative.

Barium enema

This test will be done in the hospital x-ray department.

It’s important that the bowel is empty so that a clear picture can be seen.

Your doctor or nurse will give you an instruction sheet before the test. On the day before the test, you will be asked to drink plenty of fluids and to take medicine (a laxative) to empty your bowel. Usually, on the morning of your enema, you shouldn’t have anything to eat or drink. This may vary slightly from hospital to hospital.

Just before the test, to make sure that the bowel is completely clear, you may be given a bowel wash-out. The nurse will ask you to lie on your left side while a tube is gently passed into your back passage. Water is then passed through the tube.

You will be asked to hold the liquid in the bowel for a few minutes before you go to the toilet.

For the barium enema, a mixture of barium (which shows up on x-ray) and air is passed into the back passage in the same way as the bowel wash-out. It’s important to keep the mixture in the bowel until all the x-rays have been taken. The doctor can then watch the passage of the barium through the bowel on an x-ray screen. Any abnormal areas can be seen.

The test can be uncomfortable and tiring, so it’s a good idea to arrange for someone to travel home with you if possible.

For a couple of days after your enema, you may notice that your stools are white. This is the barium being removed from the body and is nothing to worry about. The barium can also cause constipation, and you may need to take a mild laxative for a couple of days after your test.

CT colonography

This is a newer test that is also called a virtual colonoscopy. It isn’t widely available, so if you need one you may have to travel to a specialist centre. Instead of having a colonoscope put into your bowel, a computer uses CT scanning| images to examine your bowel. Sometimes a CT colonography is done instead of a barium enema. It is still being researched as a way of diagnosing bowel cancers. Your doctor or nurse can discuss it with you further.

The preparation is the same as if you were having a colonoscopy, so you will be asked to drink fluids and take a laxative. CT colonography is done in the hospital CT scanning department and can usually be done as an outpatient. 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 on your front. The computer then matches up the two scans to create a ‘virtual’ image of the inside of your bowel. You may still have a colonoscopy (see above) if biopsies are needed.