Preparing for tests and scans

There are lots of different tests and scans that are used to help diagnose cancer. Some of these tests are also used during treatment and as part of your follow-up care. Many of these tests will not affect your diabetes. But you should contact the hospital before the test and tell them that you have diabetes. They can give you advice.

Some tests will take a few hours. When you contact the hospital, ask how long you will need to be there. You can then plan ahead so that you have everything you need with you. This could include your diabetes equipment and some food.

Some tests need a bit more planning. For example, you may need to stop eating for a few hours before the test. Or you may need to follow a careful diet so that you have an empty bowel.

The hospital staff will let you know how to prepare for the tests. You may need to go into hospital the day before. You can ask your diabetes team for more advice too.

If your blood sugar level goes too low (below 4 mmol/l) at any time before the tests, you should eat or drink a fast-acting carbohydrate. This could include glucose tablets or Glucojuice®. You should take some glucose tablets with you when you go to the hospital.

Not eating before a test

You may be asked not to eat for a few hours before some tests. This could be before an MRI scan or a CT scan.

Not eating may be a problem for some people with diabetes. Because of this, you may have a shorter time when you cannot eat than people who do not have diabetes.

The hospital staff will tell you when you can eat and when to take your diabetes medicines. It is important to follow this advice carefully. They should also give you an early morning appointment. This will help shorten the amount of time when you cannot eat.

If you use an insulin pump

CT and MRI scanners and some x-rays can affect the way your insulin pump works. If you use an insulin pump, it may need to be removed before the scan or x-ray starts. A few days before the scan, you should tell the scanning or x-ray staff that you have an insulin pump.

Some procedures take more than an hour. If your pump is removed, you may need to have injections of a short-acting insulin during this time. Ask the staff how long your scan or x-ray will last. This will help you plan how to control your diabetes. Your diabetes team can also give you advice.

Having a colonoscopy or a barium x-ray

A colonoscopy and a barium x-ray look at the lining of the bowel from the inside. The bowel needs to be completely empty, so you will need to follow a careful diet before the test. You will not be able to eat for a few hours before the test. You will also need to take a laxative.

The staff doing the test can give you information on controlling your blood sugar before, during and after the test. It is important to follow this advice. Contact your diabetes team if you are not sure how to manage your blood sugar during the procedure.

You should also be given a morning appointment for these tests. This helps to shorten the amount of time you cannot eat and drink. Contact the hospital if you have been given an afternoon appointment. It might be possible to change the time.

Having a PET scan or a PET-CT scan

A PET scan uses low-dose radioactive sugar to measure the activity of cells in different parts of the body. A PET scan is often combined with a CT scan. This is called a http:PET-CT.

About 2 hours before the scan, you have an injection of a sugary fluid that has a small amount of radioactivity. The injection is given into a vein. This is usually in your arm. Cancer cells are usually more active than normal cells, so they take up more of the radioactive sugar. The sugar helps the cancer cells show up on the scan.

How well the PET scan works depends on how well your diabetes is controlled:

  • If your blood sugar level is high, the cancer cells may not take up much of the radioactive sugar. This is because they already have enough sugar from your blood. If the cancer cells do not take up the radioactive sugar, they will not be seen on the scan.
  • If the amount of insulin in your blood is high, your normal cells will take up more of the radioactive sugar. This means the cancer cells take up less sugar and do not show up on the scan as clearly.

Before a PET scan, your blood sugar level is checked. If the blood sugar level is too high, the scan may have to be moved to another day.

A few days before your PET scan, you should tell the scanning department that you have diabetes. They will give you information about:

  • what and when to eat
  • which diabetes medicines to take in the days before the scan
  • what food and diabetes medicines you should take with you to the hospital.

It is important that you follow this advice carefully.

The amount of radioactive sugar you are given is small. It should not affect your diabetes.

Scans using a dye (contrast medium)

Some types of scan include having an injection of a dye. This dye makes some areas of the body show up more clearly. The dye is known as a contrast medium. It is used in many different types of scan, including:

A contrast medium can temporarily affect how your kidneys work. This can be a problem if you take the diabetes medicine metformin. If you do, you will be asked not to take it on the day of your appointment and for about 2 days afterwards. You will be given information about when to take it and how to manage your blood sugar during this time.

This information was produced in partnership with Diabetes UK.
In partnership with Diabetes UK. Know diabetes. Fight diabetes.
Image: Diabetes UK