Further tests after diagnosis

If you have been diagnosed with rectal cancer, you will have tests to find out the size and position of the cancer. The tests will also show if the cancer has spread. The results will help you and your doctor decide on the best treatment for you.

Your blood may be tested for a protein called carcinoembryonic antigen (CEA). If the level of CEA is high, your doctors will check it regularly to see how well your treatment is working.

You will have a CT scan, which uses x-rays to see whether the cancer has spread outside the rectum. You will also have an MRI scan. This uses a magnet to build up a picture of the inside of your body. Some people may have an endorectal ultrasound, which uses sound waves to show the cancer in the rectum. Or you may have a PET/CT scan, which uses low-dose radiation to identify areas of cancer.

It may take up to two weeks for all your test results to be ready. This can be a stressful time. You may find it helpful to talk about your worries with someone close to you.

Further tests

If any of your biopsies show that there is cancer in the rectum, you will have more tests. These are to find out the size and position of the cancer and whether it has spread. This is called staging. The results will help you and your doctor decide on the best treatment for you. Some tests may be repeated during and after treatment to check your progress. Your doctor or specialist nurse will explain this to you.

You will usually have blood tests, a CT scan and an MRI (magnetic resonance imaging) scan. Some people also have an endorectal ultrasound or a PET-CT scan.


Blood tests

You will have blood tests to assess your general health. Your blood may be tested for a protein called carcinoembryonic antigen (CEA). Some people with bowel cancer have higher levels of this protein. If your level of CEA is high, your doctors may check it regularly to see how well your treatment is working.


CT (computerised tomography) scan

A CT scan takes a series of x-rays, which build up a three-dimensional picture of the inside of the body. The scan takes 10–30 minutes and is painless. It uses a small amount of radiation, which is 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.

CT scan
CT scan

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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. It’s important to let your doctor know if you are allergic to iodine or have asthma, because you could have a more serious reaction to the injection.

You’ll probably be able to go home as soon as the scan is over.

Someone having a CT scan

Having a CT scan

A radiographer explains how a CT scan works, and Jyoti talks about her experience.

About our cancer information videos

Having a CT scan

A radiographer explains how a CT scan works, and Jyoti talks about her experience.

About our cancer information videos


MRI scan

This test uses magnetism to build up a detailed picture of areas of your body. The scanner is a powerful magnet so you may be asked to complete and sign a checklist to make sure it's safe for you. The checklist asks about any metal implants you may have, such as a pacemaker, surgical clips, bone pins, etc. You should also tell your doctor if you've ever worked with metal or in the metal industry as very tiny fragments of metal can sometimes lodge in the body. If you do have any metal in your body it's likely that you won't be able to have an MRI scan. In this situation another type of scan can be used.

Before the scan, you'll be asked to remove any metal belongings including jewellery. Some people are given an injection of dye into a vein in the arm, which doesn't usually cause discomfort. This is called a contrast medium and can help the images from the scan to show up more clearly. During the test you'll lie very still on a couch inside a long cylinder (tube) for about 30 minutes. It's painless but can be slightly uncomfortable, and some people feel a bit claustrophobic. It's also noisy, but you'll be given earplugs or headphones. You can hear, and speak to, the person operating the scanner.


Endorectal ultrasound scan (ERUS)

This test may be used to help plan your operation. Ultrasound scans use sound waves to build up a picture of body tissues. An endorectal ultrasound scan can show the size and location of a cancer in the rectum.

For the test, you lie on your left side with your knees bent up. A nurse or doctor gently passes a small, lubricated probe into the back passage. This produces an image of the rectum on a screen.

The scan takes about 10 minutes and you can usually go home as soon as it is over.


PET-CT scan

This is a combination of a CT scan, which takes a series of x-rays to build up a three-dimensional picture, and a positron emission tomography (PET) scan. A PET scan uses low-dose radiation to measure the activity of cells in different parts of the body.

PET-CT scans give more detailed information about the part of the body being scanned. You may have to travel to a specialist centre to have one. You can't eat for six hours before the scan, although you may be able to drink. A mildly radioactive substance is injected into a vein, usually in your arm. The radiation dose used is very small. The scan is done after at least an hour’s wait. It usually takes 30–90 minutes. You should be able to go home after the scan.


Waiting for test results

Waiting for test results can be a difficult time. It may take from a few days to a couple of weeks for the results of your tests to be ready. You may find it helpful to talk with your partner, family or a close friend. Your specialist nurse or one of the organisations listed on our database, can also provide support. You can also talk things over with one of our cancer support specialists on 0808 808 00 00.

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