Contrast Allergy Protocols

Medical procedures such as CT scans or heart catheterizations may require injection of contrast material. These imaging tests have greatly improved diagnosis and treatment of serious medical conditions. Unfortunately, according to the American College of Radiology, 5 to 15 percent of people will have an allergy or allergic-like reaction (hypersensitivity) to the contrast. The overwhelming majority of these reactions will be mild and easy to treat.



Most institutions have protocols in place, prescribed and supervised by a physician, to prevent a reaction if you have had a contrast allergy in the past or are at risk.

Recognizing a Contrast Allergy

• A rash with hives, also known urticaria, is a sign of an allergy.

  Recognizing a reaction is the first step in the protocol. Most allergies or reactions to contrast material involve only minor symptoms, and most will occur within the first half hour after the contrast is injected.

  The most common mild symptom is hives with itching. Nausea, vomiting, chills or headache may also occur. A more severe reaction can involve wheezing (bronchoconstriction) and swelling of the throat as well as a change in heart rate. The worst type of allergy is anaphylaxis which may lead to shock. In addition to the previous signs and symptoms, anaphylaxis can be life-threatening since breathing can become difficult and blood pressure can drop to dangerously low levels.

  If you have ever had any type of reaction to contrast before, relay this information when you schedule your appointment for the test and remind the staff on the day of the test.

Preventing a Contrast Allergy

• You may be given a prescription to prevent an allergic reaction.

  If you have had a hypersensitivity reaction to contrast in the past or if your doctor determines you have other risk factors, you may be prescribed a regimen of medicine to take in the days before your test.

  The protocol usually involves diphenhydramine, a common histamine-blocking allergy medicine and a steroid medicine such as prednisone which is by prescription only. Sometimes other drugs may be added. While different institutions vary the protocol, a common regimen uses 50 milligrams of prednisone at 13 hours and 7 hours prior to the test. A final 50 milligram prednisone dose is given one hour before the study and diphenhydramine, also 50 milligrams, is added at this time as well.

Treating a Contrast Allergy

• When an allergy happens during a procedure, IV medications treat it promptly.

  If your procedure is an emergency or if you have an unexpected reaction and didn't receive premedication, intravenous medications will be used to treat you based on the symptoms. It is very important to tell the technician or nurse if you feel itchy, have trouble swallowing or become short of breath or light-headed after the contrast has been injected.

  If you get these symptoms, anti-allergy medicines such as diphenhydramine and steroids work very quickly through the IV. Inhaled medications relieve wheezing by dilating (relaxing) the airways. Your blood pressure is monitored closely and any serious drops are promptly addressed with medication such as epinephrine (adrenalin). So be assured that while there are small risks to these procedures, there are also professionals ready to make sure you stay safe.