Medicine
Exact name, dose if known, indication, time to symptoms, other medicines taken, treatment received, report and photographs.
SOS Allergo · I understand & manage
Tests & allergy assessment
Preparing for allergy tests
What to do before a skin prick test, intradermal test, patch tests, blood test or challenge test
Allergy tests do not all require the same preparation. Depending on the planned test, some medicines may affect the results while others have no effect. Your history, photographs and documents are often as important as the test itself. Instructions from the team performing your tests always take priority.
In this sheet
The most important message
Never change your medicines by yourself before a test. Some treatments may interfere with certain skin tests, but instructions depend on the medicine, type of test, clinical context and department protocol. If in doubt, contact the team before your appointment.
4 essential points
Check the instructions you received
Letter, text message, email or document from the department: these instructions take priority over any general information.
List all your treatments
Prescription and over-the-counter treatments: antihistamines, corticosteroids, inhalers, biological treatments, eye drops, creams, supplements and others. Do not decide by yourself which to stop.
Prepare the history of your reaction
If possible, record the date, suspected product, time to symptoms, symptoms, treatment received, photographs and medical report.
A test is never interpreted on its own
A positive test does not equal a clinically relevant allergy. It may show sensitisation. The doctor then checks whether it matches your symptoms, their timing and the exposure.
Does a larger test mean a more severe allergy?
No. The size of a skin prick test or another skin reaction cannot, on its own, predict the severity of a future reaction.
Skin prick tests: mainly investigating immediate allergies
A skin prick test involves placing small amounts of allergens on the skin and making a very superficial prick. The result is usually read about 15 to 20 minutes later.
Before the test
- follow the instructions you received about antihistamines;
- do not choose the withdrawal interval yourself;
- report all other medicines;
- never interrupt essential treatment without medical advice;
- report severe eczema or skin that may be difficult to test.
During and after
Positive and negative controls are usually used to check that the test can be interpreted correctly. A small local reaction may persist for a while. The wheal size alone does not predict the severity of a future reaction.
I took my antihistamine by mistake
Do not automatically miss the appointment. Simply report the medicine name, dose and time or date of the last dose. The team will decide whether the test can be interpreted, whether another method should be used or whether postponement is preferable.
Intradermal testing: a more specialised test
An intradermal test (IDT) involves injecting a very small amount of a product into the skin. It may be used in selected specialist assessments, including some medicines or Hymenoptera venoms depending on the context.
Before the test
- follow the department’s medicine instructions;
- bring precise information about the initial reaction;
- report poorly controlled asthma or a recent acute illness;
- list every treatment taken recently.
Important
An IDT result must be interpreted with the clinical history, tested product, concentration used and reading time. A positive IDT is never interpreted in isolation.
Patch tests: different preparation
Patch tests mainly investigate delayed contact allergy. They do not investigate respiratory or food allergies in the same way. Several readings may be required.
Before application
- report creams or treatments applied to the back or tested area;
- report corticosteroids and other immunomodulatory treatments;
- avoid oily products on the area if you have been asked to do so;
- report a severe eczema flare;
- report significant recent sun exposure.
Bring the requested products
Depending on the problem being investigated, the team may ask you to bring cosmetics, creams, shampoos, gloves, dressings, glues, adhesives, workplace products, packaging or ingredient lists.
For a work-related problem
If possible, bring precise product names, labels, compositions and safety data sheets when available.
During patch testing
- keep the area dry according to the centre’s instructions;
- avoid heavy sweating;
- avoid activities that may loosen the devices;
- do not scratch;
- do not reposition a fully detached patch by yourself without instructions.
The test does not end when the patches are removed
Reactions may appear gradually. Late readings can sometimes identify a reaction that was not visible at removal. Attend every scheduled reading appointment.
Blood test: specific IgE
A blood test can look for specific IgE directed against certain allergens. It may be useful when skin tests cannot be performed, are difficult to interpret or a specific question requires blood analysis.
Do antihistamines interfere with specific IgE blood tests?
No. They may interfere with some immediate skin tests, but they do not prevent specific IgE testing in blood.
Why is not ‘everything’ tested?
An allergy assessment begins with your history. The doctor then selects allergens that can answer a specific question. Testing many allergens without context may reveal sensitisation that does not explain your symptoms.
Sensitisation does not equal clinically relevant allergy
A positive result shows that your immune system recognises an allergen. It is still necessary to check whether that allergen genuinely matches your symptoms, their timing and your exposure.
Challenge tests: preparation decided case by case
A challenge test involves controlled administration of a food, medicine or, in some contexts, another product according to a medical protocol.
Never reproduce a challenge test at home
A challenge test is performed after risk assessment, using a precise protocol, monitoring and treatment facilities if needed.
Before the test
Follow the department’s exact instructions about medicines, meals or fasting, arrival time and the expected duration on site.
Contact the team if, before the appointment, you develop:
fever · an acute illness · worsening asthma · a new treatment · an unusual medical problem.
Frequently asked questions
- My test is positive: does that mean I am definitely allergic?
- No. It shows sensitisation that must be compared with your history.
- The larger my skin prick test, the more severe my future reaction will be?
- No.
- I forgot to stop my antihistamine: is my appointment wasted?
- Not necessarily. Tell the team.
- Can I stop all my treatments to make the tests work better?
- No.
- Do patch tests and skin prick tests investigate the same thing?
- No. They investigate different mechanisms.
- Can I repeat a challenge test at home?
- No.
- All my tests are negative: does that mean my symptoms are not real?
- No. Negative tests may lead to investigation of other mechanisms, diagnoses or tests.
What to bring depends on your history
Food
Exact food, amount, raw/cooked, meal composition, timing, physical activity, other cofactors and treatment received.
Venom
Suspected insect if known, circumstances, timing, symptoms, treatment and emergency report.
Eczema / contact
Photographs, products, packaging, compositions, gloves, glues, dressings and work-related context.
Respiratory
Season, place, animals, home, activity, work, treatments and circumstances of improvement or worsening.
When should I contact the department before the appointment?
- you do not know which medicines to change or continue;
- you took an antihistamine although withdrawal was requested;
- you cannot interrupt a medicine according to the instructions received;
- your asthma has worsened;
- you are unwell or have a fever;
- you have a severe eczema flare;
- you have started a new treatment;
- you did not understand the instructions for a challenge test.
Before leaving for the appointment
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Key points
- Instructions from your department always take priority over general advice.
- Never stop a medicine by yourself before a test.
- Antihistamines may affect some skin tests but not specific IgE blood tests.
- Skin prick tests, IDT, patch tests, blood tests and challenge tests do not require the same preparation.
- Your history, photographs and documents are often as important as the test result.
- A positive test is not enough to diagnose allergy on its own.
- A challenge test must never be improvised at home.
SOS Allergo resources
Main references
- Heinzerling L, Mari A, Bergmann KC, et al. The skin prick test - European standards. Clin Transl Allergy. 2013;3:3.
- Uter W, Aerts O, Agner T, et al. European Society of Contact Dermatitis Guideline for Diagnostic Patch Testing - Recommendations on Best Practice. Update 2026. Contact Dermatitis. 2026;95:237-275.
- EAACI/ENDA position paper on drug provocation testing. Allergy. 2024;79:565-579.
- Updated EAACI Statement on Drug Hypersensitivity Skin Testing: Methodology and Non-Irritative Concentrations. Allergy. 2026.