Kenneth U Ekechukwu M.D.

What if I'm allergic to contrast?

This scenario is common and many people go about in life labeled as allergic to radiocontrast (dye) without verifying if they truly have such allergy. (Radiocontrasts or dye contain high concentrations of iodine which, when it mixes with blood in the body and imaged with x-rays, makes blood and blood vessels easy to identify. Imaging with x-rays can be with fluoroscopy or CT-scan.) Because a form of allergy to dye can be fatal, patients and healthcare providers are sometimes hypervigilant and characterize any event that occurs during exposure to dye as an allergic reaction, a kind of Chicken Little syndrome, if you will. First, let us clarify the definitions of dye allergy. Broadly, there two forms: anaphylactic reaction and anaphylactoid reaction. Notice that the two terms resemble each other, but the anaphylactic reaction is the potentially deadly reaction. It is what we call in medical parlance an immediate hypersensitivity reaction, actually, a protective reaction gone awry. Because the individual was exposed to certain chemicals or chemical structures in the past, recognized by their body as foreign, certain cells loaded with reactive substrates are produced by the body and their cell membranes equipped to recognize this foreign chemical in the future. As soon as the individual is re-exposed to the foreign agent, these cells release their contents and produce systemic reactions that tighten smooth muscles around air ways, cause mucosal swelling in the throat and the airways, produce extensive hives and itching, and, importantly, cause profound drop in the blood pressure. Patients may then wheeze, be unable to breathe, have swollen tongues, itch all over, and have catastrophic drop in their blood pressure. If immediate medical care is unavailable or delayed, the victim may expire. Treatment consists of securing the airways by intubation, shoring up the blood pressure with crystalloid infusions, and administering subcutaneous of parentereal epinephrine and, sometimes, a steroid. Response is usually dramatic, especially to epinephrine. Such patients must never be re-exposed to the substance for life, if known. Anaphylactoid reaction is different. The "oid" means "resembles". It is an idiosyncratic reaction, meaning peculiar to an individual and typically presents as an itch without the melodrama of anaphylaxis. It is not usually associated with death and can be prevented by premedicating an individual with diphenhydramine (Benadryl), an anti-histamine and prednisolone (a steroid). This approach may not be universally protective, but does blunt or even prevent anaphylactoid reactions. Institutions and individuals vary in the dose and scheduling of these medications for expected exposures to radiocontrast. I give my patients Benadryl 50 mg and prednisolone 50 mg, both by mouth 13 hours and 1 hour, respectively, before the time of their procedure. Sometimes, I shore-up this with intravenous methylprednisolone (Solu Medrol) before the procedure. Sadly, this reaction can be delayed and happen when the individual has left the scene of exposure. It is, therefore, not uncommon for healthcare providers to observe people suspected to have such reactions overnight in monitored settings, when exposed to an agent suspicious agents. Now to answer the question posed. Our friend must revisit the event and narrate it to a discerning provider as well as they can to determine if the itch was or was not real. If it was minor, unaccompanied by the fanfare of anaphylactic reaction, they may receive radiocontrast after premeditation and be observed overnight in an hospital. If nothing happens, clearly, they return to the pool of the normal and can have contrast-enhanced studies, especially when such are vital to their well-being. If they are unprepared for such "experiment", then their studies may be performed with the agent used for contrast studies in MRI (gadolinium) or carbon dioxide, depending on the state of their kidneys, the expertise and sophistication of the facility doing the study, and the part of the body being imaged; we avoid the use of carbon dioxide for studies above the diaphragm, and gadolinium in patients with impaired renal function of moderate-to-severe degree. Problem is that these agents do not yield images of comparable quality as those done with radiocontrast. READ MORE