How colon and rectal cancers are diagnosed
Most people are diagnosed after going to see their GP about symptoms. If your GP suspects you may have cancer, you should be seen at the hospital within 14 days.
Some people are diagnosed after taking a test as part of the NHS Bowel Screening Programme. Bowel screening is a way of finding bowel cancer at an early stage before it causes symptoms.
Sometimes, people are diagnosed with bowel cancer after being admitted to hospital with a problem, such as bowel obstruction.
At the hospital
The specialist will ask you about your general health and any previous medical problems you’ve had. They’ll ask whether you have a family history of bowel cancer.
They will examine you, and may carry out a rectal examination. This involves the doctor placing a gloved finger into your back passage to feel for any lumps or swelling. It may feel uncomfortable, but not painful.
You will usually have a blood test to check your level of red blood cells. If you have a low number of red blood cells, this is called anaemia. You will also have blood tests to check whether your liver and kidneys are working normally.
The main test used to look for bowel cancer is a colonoscopy.
Other tests that are sometimes used to diagnose bowel cancer include:
A colonoscopy looks at the inside of the whole length of the large bowel. You can usually have this test as an outpatient. It takes about an hour.
Your bowel has to be completely empty for a colonoscopy. You will be given instructions on what you can eat and drink the day before the test. You’ll also be given a medicine (laxative) to take to empty your bowel.
Just before the test, you may be given a sedative into a vein (intravenously) to help you feel more relaxed 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. There is a tiny light and camera on the end of the colonoscope. During the test, the doctor or nurse will use this to photograph any areas of the bowel that look abnormal. They may also take samples (biopsies) from these areas. The biopsies will be sent to the laboratory to be checked for cancer cells.
Most people are ready to go home a couple of hours after having a colonoscopy. You’ll need someone to collect you from the hospital, as you should not drive for 24 hours after a sedative.
Virtual colonoscopy (CT colonography, CT enema, CT pneumocolon)
In this test, a CT scanner takes a series of x-ray pictures of your bowel. A computer then puts the pictures together to make a three-dimensional picture of your bowel. This test may be done instead of a colonoscopy, or it may be done if the colonoscopy didn’t give a clear enough picture.
A virtual colonoscopy is done in the hospital CT department. You can usually have it as an outpatient.
Your bowel has to be completely empty for the scan. 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 what to do.
Your doctor may give you an injection of a medicine to help the muscles in your bowel relax. You may also have an injection of a dye (contrast medium) at the same time. Your doctor will tell you if you’re going to have this.
Just before the CT scan, 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.
This test looks at the inside of the rectum and the part of the colon closest to the rectum (the sigmoid colon). You can usually have it done as an outpatient.
A sigmoidoscope is a tube with a light and camera on the end. You lie curled on your left side and a doctor or nurse passes the tube into your back passage. 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 need the toilet, but the feeling will gradually go away once the test is over.
During the test, the doctor or nurse will take samples of tissue (biopsies) from any areas of the colon that look abnormal. This is painless.
You should be able to go home as soon as the test is over.
Waiting for your test results
It will probably take several days for the results of your tests to be ready and this waiting period will obviously be an anxious time for you. It may help if you can talk things over with a relative or close friend. You may wish to ring our cancer support specialists or one of the organisations listed in the further resources section.