If the biopsy shows that there is a cancer in the large bowel, further tests are often needed to find out the size and position of the cancer, and to see whether it has spread. This process is called staging, and may take some time. The results will help you and your doctor to decide on the best treatment for you. Sometimes, during and after treatment, these tests may be done again to check on your progress.

Although tests are useful in diagnosing bowel cancer, no single test can give all the necessary information. For example, sometimes even modern scans can’t pick up tiny areas of cancer. Occasionally, other medical conditions show similar results, making it difficult to decide what is and is not cancer. Doctors have to think about all the information they get from the different tests and examinations, along with your symptoms and medical history. For this reason, it is often best for the doctor to discuss test results with you personally.

The following additional tests are most often used with cancer of the large bowel.

You will probably have blood tests to assess your general health, and also to check for a particular protein that is sometimes produced by bowel cancer cells. The protein is called carcinoembryonic antigen (CEA) and is also known as a 'tumour marker'.

Chest x-rays are often taken to check the health of your heart and lungs.

An ultrasound scan uses sound waves to look at internal organs, such as the liver and the inside of the abdomen, to see whether the cancer has spread to other organs. You will usually be asked not to eat or drink for at least six hours before the test. Once you are lying comfortably on your back, a gel is spread onto your abdomen. A small device that produces sound waves is passed over the area. The sound waves are then converted into a picture by a computer. The test only takes a few minutes.

In some situations you may have a probe (like a tube) inserted into the rectum to produce ultrasound scans. This is known as an endoscopic ultrasound (EUS).

A CT (computerised tomography) scan takes a series of x-rays, which builds up a three-dimensional picture of the inside of the body. It can show the size of the tumour in the bowel and whether it has spread beyond the bowel. The scan is painless but takes longer than an ordinary x-ray (from 10–30 minutes). CT scans use a small amount of radiation, which will be very unlikely to harm you and will not harm anyone you come into contact with. You will be asked not to eat or drink for at least four hours before the scan.

You may be given a drink or injection of a dye, which allows particular areas to be seen more clearly. This may make you feel hot all over for a few minutes. If you are allergic to iodine, or have asthma, you could have a more serious reaction to the injection, so it is important to let your doctor know beforehand.

Just before the scan, a similar liquid is also passed into your back passage through a small tube. Although this may be unpleasant at the time, it makes sure that the best possible picture is produced. Once you are in position, the scan will be taken.

You will probably be able to go home when the scan is over.

PET (positron emission tomography) scans are a newer type of scan and you may have to travel to a specialist centre to have one. They are not always necessary but you can discuss with your doctor whether one would be useful in your case. PET scans can be used to accurately define the cancer and find out if it has spread to other parts of the body.

A PET scan uses low-dose radioactive glucose (a type of sugar) to measure the activity of cells in different parts of the body. A very small amount of the mildly radioactive substance is injected into a vein, usually in your arm. A scan is then taken a couple of hours later. Areas of cancer are usually more active than surrounding tissue and show up on the scan.

Sometimes a PET scan is combined with a CT scan – this is called a PET/CT scan. A small amount of a radioactive substance is injected in the same way as a standard PET scan, and then the CT scan takes a series of x-rays. The scanner combines the two different types of information and allows your doctor to measure any changes in the activity of cells and to know exactly where in the body the changes are. A PET/CT scan can be used to show whether the cancer has spread and to give accurate information that will help the doctors decide on the best treatment.

It will probably take from several days to a couple of weeks for the results of your tests to be ready. The results of the tests will show the grade and the stage of the cancer. This information will be used by a team of doctors and nurses, known as the multi-disciplinary team or MDT, to decide on the most appropriate treatment.

Waiting for results can be a difficult time and you may need support from a support organisation.