Contrast medium allergy

Introduction

Contrast media are used for various imaging procedures in medicine, for example in a CT, MRI, ultrasound or angiography to assess blood vessels. Contrast medium is often administered intravenously. The contrast medium then spreads into the blood vessels and accumulates, especially in areas with good blood circulation.

This is helpful, for example, in the case of a malignant tumor with a good blood supply. However, contrast medium can also be used to better visualize inflammation foci. Overall, as the name suggests, the contrast medium increases the contrast, so that structures can be better distinguished from each other. An allergy is present when the body recognizes a component of the contrast medium, such as the frequent ingredient iodine, as an allergen. The allergen then binds to certain cells of the immune system, which leads to the release of substances that mediate an allergic reaction.

Causes

Since many contrast media contain iodine, a contrast medium allergy can occur, for example, in the course of an existing iodine allergy. Asthmatics, for example, are more susceptible to contrast medium allergies, as they have an increased allergic potential. This applies not only to asthmatics but also to people who already have several allergies, such as food allergies or hay fever.

Also persons with a Neurodermitis form more frequently a contrast medium allergy or generally allergies. In addition, taking a beta-blocker increases the risk of developing a contrast medium allergy. Fortunately, in most cases a contrast medium allergy only manifests itself with a slight reaction.

For example, a skin rash due to allergy may occur, accompanied by itching. Furthermore, nausea, dizziness or headaches may also occur. The symptoms can either develop immediately after the administration of the contrast medium (maximum within one hour = allergy of the immediate type) or they only appear a few days after contact with the contrast medium.

During an imaging session, you will usually be advised by the staff caring for you to report coughing, sneezing or itching, as well as swelling of the mucous membranes, shortness of breath or a skin rash, as these may be signs of an allergic reaction. If it is not a mild allergic reaction but a moderate reaction, symptoms such as a mild shortness of breath, an accelerated heart rate, nausea or vomiting, fluid retention in the tissues (edema) or hives may also be present. The edema is often located on the face in the case of an allergic reaction.

Swelling can also occur in the area of the mucous membrane. If a swelling of the mucous membrane occurs within the respiratory tract, there is a risk of suffocation. In extreme cases, a severe allergic reaction can occur, resulting in a so-called anaphylactic shock.

Anaphylactic shock is the most severe, life-threatening form of allergy. Due to the allergic reaction, all blood vessels suddenly dilate, which leads to an enormous drop in blood pressure. If an anaphylactic shock is not treated with medication in time, in some cases it can also lead to circulatory failure.

A typical consequence of an allergy to contrast media is an itchy skin rash, a so-called urticaria, or hives. Typically, hives are already visible to the naked eye, i.e. white to reddish thick and swollen areas of the skin, but these are quite well defined. Besides the contrast agent allergy, urticaria can have many other causes, but allergies of any kind are among the most common triggers of this skin reaction. Hives is therefore a well-known dermatological symptom.