What is a contrast medium and what is it used for?
As part of a number of examinations, you may need to have an injection of a contrast medium. This is a colourless dye that shows up on x-ray pictures and scans, and is used to highlight structures in the body that can't be seen without it.
What are the risks?
This contrast agent causes no complications in the vast majority of people who are injected with it. However, there are risks involved with any medical procedure and, in a small number of people, certain side effects can occur following an injection of contrast agent.
Many people describe a feeling of warmth around their body and an unusual taste in the mouth. This is normal, and lasts for a minute or two. Brief nausea may occur. Some people develop minor allergic symptoms, such as hives, itchiness or a stuffy nose.
There is a tiny risk of a more serious reaction: rarely, more serious allergic symptoms may require medical treatment, and severe asthmatics can occasionally become wheezy after an injection of contrast agent. With the modern agents we use, the risk of these things happening is very low. Your doctor who requested this test will be aware of the risks, and has recommended the test knowing the benefits of the examination far outweigh the tiny risk involved.
If you have:
- had a previous allergic reaction to a contrast medium
- a strong history of allergies
- kidney failure
then please discuss this with the staff when you make the appointment and when you come for your radiology test. The radiologist may suggest you have another radiology examination that doesn't require contrast media, or suggest you take a medication, eg, an antihistamine, prior to your appointment.
Do you take Metformin?
An association has been found between the intravenous administration of contrast media and lactic acidosis in patients with diabetes who are taking Metformin. The association is rare, and occurs in patients with impaired kidney (renal) function. If you have an examination needing contrast medium, you should discuss stopping Metformin before your study but you must not do this without the advice of your doctor. Your doctor and the radiologist will discuss the best method of imaging to meet your needs.
Examinations that use contrast medium:
- some CT examinations
- some MRI examinations
- micturating cystogram - using a fine tube, contrast media is used to fill the bladder, eg, used for children with recurrent urinary tract infection
- sialography - to view the salivary glands, e,g looking for a calculus
- dacrocystography - to view the tear ducts
- arthrograms - where contrast media is injected into the joint (eg, shoulder, knee). This test may be done in conjunction with MRI.