Medicine

Patient information for Translation

DRUG ALLERGY TESTING

This information sheet explains what to expect when you have drug allergy testing at St. Bartholomew’s Hospital. If you have any questions or concerns, please do not hesitate to contact the Allergy Nurse Specialists – details are at the end of this information sheet.

What is a drug allergy test?

Drug allergy testing involves having either skin tests followed by a challenge test, only skin tests, or only a challenge test.  The drugs tested are either the ones suspected of triggering your allergic reaction, or different drugs which are tested to see if they are safe alternatives.

How are skin tests done?

Skin tests are usually two-step processes: skin prick tests and intradermal skin tests.

For skin prick tests a drop of solution of each of the drugs to be tested is put on the skin of your forearm.  A lancet (fine needle) is used to lightly prick your skin through the solution. After 15 minutes, the site is inspected to check for any reactions. A positive reaction is when the skin around the needle prick becomes itchy, red and develops a swelling which usually disappears within 30-60 minutes. A negative reaction is when the skin remains normal.

If the skin prick test is negative, you may go on to have an intradermal skin test. For this test a very small amount of the drug (0.03ml) is injected just below the skin in your forearm to create a small bleb (swelling). A positive reaction will cause an increase in the size of the bleb with redness and itching. A negative result does not produce any reaction.

You may go on to have a challenge test if skin tests are negative. If the skin tests are positive, you will not need a challenge test.

What is a challenge test?

A challenge test is when we give you a drug under close medical supervision to find out if you are allergic to it or not. This is done by giving you gradually increasing doses of the drug, over a certain amount of time, until an allergic reaction occurs or the ‘top dose’ is taken without any adverse reaction. The drugs are usually given by mouth (orally) but for certain drugs they are given in the vein (intravenous), muscle (intramuscular) or below your skin (subcutaneous).

What are the benefits of having a skin test / challenge test?

The skin test and challenge test will confirm whether you have a drug allergy or not. This may help you to confidently take the medication without fear of reacting to the drug tested.

If we find that as a result of the skin tests or challenge tests, you are allergic to a particular drug, you will then be able to exclude that drug. 

Are there any risks associated with having a skin test / challenge test?

There is a risk that you will have a reaction to the drug you are being tested for – this is why these tests are done in a hospital setting. You will be closely watched by an allergy nurse specialist who will monitor for any signs of allergic reaction. Reactions tend to be mild and include itching, rash, swelling. Sometimes people experience more severe reactions including throat tightness, difficulty breathing, light-headedness/dizziness. A doctor is present during the testing to treat you if needed.

If you do have an allergic reaction the testing will be stopped. Medicine will be given to relieve the symptoms and to stop the reaction from getting worse – this may be antihistamines, (explain in plain English) steroids or, in a severe reaction, adrenaline injection may be given.

Are there any alternatives?

You may choose not to have drug allergy testing and continue to avoid the drug you might be allergic to. However, these tests are the only safe and definitive way to find out whether you have a drug allergy or not.

What should I do to prepare for the skin test and challenge test?

You need to spend a half day in the ward so please have your breakfast or lunch before the appointment as you will not be able to have anything, except water, until the end of the test.

What happens during the drug allergy testing?

On arrival you will be seen by the allergy nurse specialist who will take your pulse, blood pressure and peak flow (breathing test). Your nurse will continue to monitor these throughout the session. The challenge procedure will be explained to you, including the risks and benefits. Your consent needs to be obtained before the test. Please do not hesitate to ask the nurses or doctors any questions you may have.

On rare occasions, a cannula (small plastic tube) may be inserted in the back of your hand or inner elbow before the challenge – this allows us to give medicines and fluids quickly if needed. The need for this will have been discussed at your clinic appointment. We will talk with you about this before the procedure.

You will then have the skin tests and / or challenge tests depending on the drug being tested.

You will be checked for signs of an allergic reaction before each dose of a drug is given. If you have an allergic reaction at any point the test will be stopped immediately. The nurse will treat you according to the type of reaction, and the doctor will be called to check you.

What happens after the drug allergy testing?

Positive test: This is when there is a reaction during skin testing or the challenge test. A positive reaction means you are allergic and need to strictly avoid that drug and other drugs in the same group. Our doctors and nurses will treat the reaction as needed, and you will be watched for a few hours after a reaction. Occasionally, you may need to stay in hospital overnight.

Negative test: This is when no reaction occurs during skin testing or challenge test. You will need to stay with us for one to two hours after the final dose of the drug is given to make sure there is no delayed reaction.

Delayed positive test: Delayed reactions on skin test sites or elsewhere after leaving the hospital are rare and are usually mild. If you get a delayed reaction it suggests you have a delayed-type allergy to the drug.

What do I need to do after I go home?

If you have had a positive reaction we will speak and write to you and your GP about the importance of you avoiding that drug and other drugs in the same category. We recommend getting a medical alert bracelet to inform healthcare professionals in future in case you are unable to. This can be obtained from www.medicalert.org.uk or other online sources.

We will give you written information on delayed reactions and advice on what to look out for and what to do, before you leave the hospital.

If you don’t get any reaction (immediate or delayed), it confirms you are not allergic to the drug.

Are there any follow up appointments?

We will talk with you about this during the skin test / challenge visit if you need further skin tests or challenge tests. We will also let you know if you will have a further clinic appointment. The nurse or doctor will talk with you about any changes in your treatment before you go home. We will send your GP a letter with information about the skin test / challenge result and you will receive a copy of this letter.

Further information

If you have any questions or concerns, please contact the Allergy nurse specialists (Monday to Friday 9am-5pm) on Tel:  0203 465 6387 or 07720 948 385 or Email: bartshealth.adultallergynurses@nhs.net

Please arrive 15 minutes before your appointment or your test may have to be postponed. If you need to rearrange the appointment, please contact the Allergy Coordinator (Monday to Friday 9am-5pm) on Tel: 0203 765 8584 or Email: adultallergy.bartshealth@nhs.net Please let us know as soon as possible so that we can offer the slot to someone else.  

Large print and other languages
This information can be made available in alternative formats, such as easy read or large print, and may be available in alternative languages, upon request. For more information, speak to your clinical team.
 

এই তথ্যগুলো সহজে পড়া যায় অথবা বৃহৎ প্রিন্টের মত বিকল্প ফরম্যাটে পাওয়া যাবে, এবং অনুরোধে অন্য ভাষায়ও পাওয়া যেতে পারে। আরো তথ্যের জন্য আপনার ক্লিনিক্যাল টিমের সাথে কথা বলুন।

Na żądanie te informacje mogą zostać udostępnione w innych formatach, takich jak zapis większą czcionką lub łatwą do czytania, a także w innych językach. Aby uzyskać więcej informacji, porozmawiaj ze swoim zespołem specjalistów.

Macluumaadkaan waxaa loo heli karaa qaab kale, sida ugu akhrinta ugu fudud, ama far waa weyn, waxana laga yabaa in lagu heli luuqaado Kale, haddii la codsado. Wixii macluumaad dheeraad ah, kala hadal kooxda xarunta caafimaadka.

Bu bilgi, kolay okunurluk veya büyük baskılar gibi alternatif biçimlerde sunulabilir, ve talep üzerine Alternatif Dillerde sunulabilir. Daha fazla bilgi için klinik ekibinizle irtibata geçin.

یہ معلومات متبادل فارمیٹس میں دستیاب کی جا سکتی ہیں، جیسا کہ پڑھنے میں آسان یا بڑا پرنٹ  اور درخواست پر متبادل زبانوں میں بھی دستیاب ہو سکتی ہیں۔ مزید معلومات کے لیے، اپنی کلینکل ٹیم سے بات کریں'۔

Patient Advice and Liaison Service (PALS)

Please contact us if you need general information or advice about Trust services: www.bartshealth.nhs.uk/pals

Tell us what you think

Tweet us @NHSBartsHealth
Talk to us via facebook.com/bartshealth
Leave feedback on NHS Choices www.nhs.uk

Reference: BH/PIN/1108

Publication date: Nov 2021

All our patient information leaflets are reviewed every three years.

©Barts Health NHS Trust

Switchboard: 020 7377 7000

www.bartshealth.nhs.uk