Diagnosis

Contrast agent allergy

introduction

Contrast media are used for various imaging processes in medicine, for example in a CT, MRT, ultrasound examination or in angiography, which can be used to assess the blood vessels.

Read more on the subject below MRI with contrast agent - is it dangerous?

Contrast media is often administered intravenously. The contrast agent then spreads in the blood vessels and accumulates, especially in areas with good blood circulation. This is helpful for a malignant tumor with a good blood supply, for example. But foci of inflammation are also better represented with contrast media.

Overall, as the name suggests, the contrast agent increases the contrast so that structures can be better differentiated from one another.

An allergy is present when the body recognizes a component of the contrast medium, such as the common ingredient iodine, as an allergen. The allergen then binds to certain cells of the immune system, which lead to the release of substances that mediate an allergic reaction.

causes

As a lot of contrast media containing iodine are, for example, a contrast agent allergy in the course of an existing one Iodine allergy occurrence.

For example, they are more susceptible to a contrast agent allergy Asthmatic, as this is an increased allergic potential have. In addition to asthma sufferers, this also applies to people who already have several allergies, such as food allergies or hay fever. Even people with a Neurodermatitis more often develop a contrast medium allergy or allergies in general.

In addition, taking a beta blocker increases the risk of developing a contrast agent allergy.

Symptoms

Fortunately, in most cases a contrast agent allergy manifests itself only with a slight reaction. For example, it comes to one Rash from allergythat of a itching is accompanied. Furthermore can also nausea, dizziness or a headache occur. Symptoms can be either right away develop after the administration of the contrast medium (maximum within one hour = immediate type allergy) or they only occur couple of days after contact with the contrast medium. During an imaging session, the caregiver will usually advise you to report if you cough, sneeze or itch, as well as swelling of the mucous membranes, shortness of breath or a rash, as these could be signs of an allergic reaction.

Is it not a mild allergic reaction, but a medium response, symptoms come like a mild one shortness of breath, one accelerated heart rate, Nausea up to Vomit, Fluid retention in tissue (Edema) or one Hives added. The edema is often on the face in an allergic reaction. Swelling can also occur in the area of the mucous membrane. Kick a Swelling of the mucous membranes within the airways, there is a risk of suffocation.

In extreme cases, there is one severe allergic reactionthat are in a so-called anaphylactic shock flows out. Anaphylactic shock is the most severe, life-threatening form of allergy. As a result of the allergic reaction, all of the blood vessels suddenly expand, which leads to an enormous drop in blood pressure. If medication is not taken in good time in anaphylactic shock, it can in some cases lead to circulatory failure.

What does the rash look like with a contrast agent allergy?

A typical consequence of a contrast agent allergy is an itchy rash, known as urticaria, or hives. Typically, you can already see wheals with the naked eye, i.e. white to reddish, thick and swollen areas of the skin that are quite well defined.

In addition to the contrast agent allergy, urticaria can also have many other causes, but allergies of all kinds are among the most common triggers of this skin reaction. Hives is therefore a well-known dermatological symptom.

Possibilities for an allergy test

If you have noticed a slight tingling sensation in your nose or itching or something similar during an examination with contrast media, a test can be carried out to check whether there is actually an allergy. This test is usually carried out as part of a so-called prick test. In the prick test, the skin of the forearm is pricked several times superficially with a small stick. Then different allergens are applied to the individual areas. If there is an allergy, the area where the allergen is located is reddened with wheals and itching.

The prick test is positive if the contrast agent allergy is an immediate reaction (type I allergy), i.e. if the symptoms occurred relatively soon after the contrast agent was administered.
But if allergic symptoms only occur after 12 to 72 hours, it is more of a type IV allergy (late type). This can be proven by means of a patch test. Various allergens are applied to the skin of the back. This area is then covered with special plasters. After 48 and 72 hours, check whether there has been a local allergic reaction in this area.

In principle, a provocation test with the allergen can also be carried out intravenously, since this entails more risks in contrast to the other two methods, the provocation test is usually not used.

Read more about this under Allergy diagnostics such as Allergy test

Treatment / therapy

In most cases, the allergic symptoms that have occurred do not require any further treatment, as these are often only mild and go away on their own. Cortisone preparations and / or antihistamines can be used to support the allergic reaction.

Read more about this under Antihistamines

If an allergic shock occurs, it is a potentially life-threatening emergency that should be treated as soon as possible. The victim should be placed in a shock position in which the person lies flat on their back and their legs are raised. If the anaphylactic shock occurs immediately during the administration of the contrast medium as an immediate reaction, the supply of the contrast medium must be stopped immediately. The drug therapy for anaphylactic shock is the administration of adrenaline and cortisone. The drugs are administered via the vein like the contrast agent. In addition to adrenaline and cortisone, antihistamines and intravenous fluids are often used. In addition to the medication, it is often necessary to provide supportive oxygen through a mask.

Read more about this under Therapy of shock

Preparation of contrast medium administration despite allergy

For some indications, even with an existing contrast agent allergy, the administration of contrast agent cannot be dispensed with, because with contrast agent the best pictures receives. If, despite the allergy, a contrast agent is necessary, the patient receives it before the examination anti-allergenic Medication.

Usually used for premedication twelve hours and two hours before the administration of contrast agent Cortisone preparation administered as a tablet. If oral administration is not possible, a drug can also six hours before investigating about the vein are fed. Immediately before the examination, additional Antagonist of histamine, a hormone that is responsible for allergy reactions, intravenous administered. Clemastine and ranitidine can be used for this.

Is it a emergency, cannot wait twelve hours to adequately administer a cortisone preparation before the examination. In this case you only use the two Antagonist of histamine directly before the administration of contrast medium.

What are the alternatives for a contrast agent allergy?

Contrast media are used in many different examinations nowadays, above all, of course, in imaging procedures. There they are often necessary or at least significantly improve the result, as they make the body structures to be examined more visible.

However, if there is a contrast agent allergy, there are two options for carrying out the upcoming examination: Firstly, certain examinations can also be carried out without contrast agent, i.e. natively. However, if the administration of contrast medium is necessary, there is a second possibility: The person concerned can then be given an infusion with a drug that blocks the allergy-triggering receptors. This medication will then work until the examination is over and the contrast agent has been flushed from the body.

prophylaxis

The best prophylaxis, of course, is the future Waiver the contrast agent to which you have had an allergic reaction. If you are allergic to a contrast agent, it does not immediately mean that you are allergic to all contrast agents. You can either use contrast media intravenous or orally take as a drinking liquid. In the oral Gabe is usually Not expect an allergic reaction. However, oral contrast media are mostly only used for contrast imaging of the gastrointestinal tract, so that the administration of an intravenous contrast medium (for displaying vessels) cannot be bypassed by oral administration.

In order to avoid a surprise for the examiner, one should definitely X-ray pass, on which the corresponding contrast agent allergy is noted, must be carried with you. It comes to one emergency and you cannot be asked about an allergy before the examination, thus avoiding a severe allergic reaction. The contrast agent allergy should be mentioned to the attending physician prior to imaging. As a rule, the doctor always asks about an existing contrast medium allergy.

The contrast media are, however, subject to strict restrictions Controls during development, these are even stricter than other drugs. Special care is taken to ensure that these have little or no allergic potential, so that contrast media are well tolerated in most cases.