Information for patients undergoing specialised allergy testing

You have been referred to the allergy clinic to find out whether you are allergic to a particular medicine, food or other substance. This requires a special appointment that may take a whole day. These appointments are in short supply, so please read the instructions. It is vital you let us know as early as possible if you cannot attend.

On the day of the appointment

It is important to have a good breakfast before you attend, as you will not be allowed to eat during the tests. This can mean that you do not eat until late in the day. Also, please bring reading material with you to help pass the time.

Procedure

When you are first seen the doctor will take a full medical history and ask detailed questions about your previous reactions. You may then undergo skin testing with foods or drugs that are considered important in your previous reaction. If this does not provide enough information then in some cases the doctors in the allergy clinic may discuss with you if you would like to undergo a challenge test to the suspected food/medicine to which you have reacted or may need in the future. Challenges are undertaken only if other ways of diagnosing your sensitivity are ineffective. In most cases, challenge tests are undertaken when it is likely the drug /food may be tolerated i.e. to exclude allergy.

The challenge may start with little or no drug/food and then continues by giving increasing doses of the drug/food. These will be given either by mouth or by injections under the skin of your arm or leg. During the challenge you will remain under observation in the clinic. The test may take most of the day. Measurements will be taken of your pulse, blood pressure and lung function. You may also be required to have a blood test during the appointment.

How long will I have to stay in the clinic?

This varies depending on the number of tests that are required and can sometimes take most of the day. If you require a challenge test it is necessary to remain in the clinic under observation after your final dose for up to two more hours. Some patients who require skin tests only or certain types of challenge may be able to leave by 14:00.

You may be able to bring one relative/friend with you during the appointment providing both of you are well.

Side effects

In most cases the challenge is negative and provides reassurance that you are safe to take a particular drug/food. If the challenge is positive, most reactions are usually mild, for example: itchiness, reddening, a nettle-type rash or swelling. Occasionally, more serious reactions can occur such as a generalised itchy rash, asthma, itchy eyes or nasal symptoms. All these are readily treatable.

Severe reactions

Challenge tests are conducted in a way that reduces the risk of a reaction. Although most reactions are mild, more severe allergic reactions can also occur during the challenge and will be treated quickly by the clinic doctor. The possibility of a reaction is the reason why it is necessary to undergo challenge in a specialised allergy clinic run by staff that are highly trained in the treatment of allergy.

Usefulness of the challenge

A positive challenge will provide useful information about drugs/foods to avoid in future. A negative challenge is also useful as it provides information about what you can take in future.

Occasionally, a negative test will mean you have to come back for further testing.

Other medications

It is important to tell the doctor which medications you are taking or if you have started a new drug. Some drugs will interfere with the challenge and therefore must be stopped before the procedure. For example, Antihistamines such as Piriton, fexofenadine, cetirizine and loratadine, must be stopped three days before your appointment. Others such as beta-blockers (for blood pressure or heart conditions) should ideally be stopped before the challenge is started.

Contact after your clinic appointment

In many cases you will be asked to telephone or email after your clinic visit to report any delayed skin test reactions or whether a course of treatment caused any side effects. You will be provided with telephone numbers and email addresses to allow you to make contact easily and so that the clinic doctor can complete his report to your referring doctor.