Iodinated Contrast
Indications
Iodinated contrast media (sometimes called "X-ray dye,"
"X-ray contrast, " "IVP dye," or "Radio Contrast
Media, RCM") is often a very
important part of your imaging exam. We use contrast for CT
scans, angiograms, or IVP exams where it is administered in the vein
(intravenous or IV). For some exams it is essential and the exam
cannot be done properly without it. For many studies it is important for
increasing diagnostic accuracy and best detection of subtle cancers or
other diseases. Your referring doctor and your radiologist will
know best when to use or omit IV iodinated contrast for your exam.
Contraindications
There are a few situations in which to avoid using
or obtain special preparation for using iodinated contrast. One of
these is poor kidney function because after the exam your kidneys have
the role of taking the contrast out of your blood stream and excreting
it into your urine. If the kidneys are functioning weakly, they
may have trouble removing the contrast and may be further damaged by it.
In normally functioning kidneys there is no damage. In patients
that have diabetes or other reason that they might have limited kidney
function, a blood test may be needed in advance to make sure they are
functioning well enough to do the exam with contrast.
As with any medication, a patient can have an
allergy to the contrast or, more often, may have an "allergic-like" reaction.
Reactions to contrast are typically mild, consisting of flushing,
nausea, hives, or itching, but they can rarely be severe and even
life-threatening. Fortunately, in the case of a severe reaction,
there is a simple, fast and effective treatment with a small dose of
epinephrine. In patients with a previous history of a reaction to
IV iodinated contrast, we can give the patient a small series of doses
of medicine to take orally the day before the exam to minimize the
chance of reaction.
The Iodine Allergy Myth
Some people that have a history of allergy to
shellfish, a history of a previous reaction to IV iodinated contrast, or
a history of a reaction to a topical iodine solution, have been told
that they have "iodine allergy." This is actually not
correct. "Iodine Allergy" doesn't really exist.
Iodine is a substance essential to life and is found
throughout your body like within thyroid hormone or in amino acids, your
body's basic building blocks. The reactions experienced in each of
these situations do not have to do with the presence of the iodine.
Instead, in each case the reaction is to another substance. In the
case of shellfish, the reaction is to tropomyosin, a muscle protein.
In the case of iodinated contrast, it is the other portion of the
contrast molecule, not the iodine. In the case of topical iodine
solution, it is to other substances in the solution, not the iodine
itself.
Shellfish allergy is not a contraindication to iodinated contrast
because the allergy is entirely unrelated. This is a longstanding
myth even within the medical community and is difficult to dispel.
To some degree, asthma will increase the possibility of a contrast
reaction. Sensitivity to Betadine® and other Iodine-containing
solutions is unrelated to reactions to iodinated radiographic contrast
agents.
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From the
American Academy of
Allergy Asthma and Immunology:
Once a person has one contrast reaction
they are at very high risk for more unless treated. The
reactions do tend to be worse in people who are dehydrated
(dried out) when they are given the contrast in their veins.
These reactions are not caused by iodine and are not more
common in people with shellfish or any other true allergy.
They can be minimized by pretreatment with antihistamines
and oral steroids and/or using non-ionic contrast material
that, interestingly, still has iodine in it. |
For more information, click
here.
Or search for "iodine" in the
Ask the Expert
page of the website of the American
Academy of Allergy Asthma and Immunology.
Additional Comments
Years ago, the only contrast agents in use were
ionic iodinated contrasts. Currently we use nonionic agents, with
a significant reduction in adverse reactions.
As for MRI contrast agents, also typically
administered IV, are gadolinium-based and unrelated to iodinated
contrast agents.
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