Skin prick tests

Some medicines, particularly those with antihistamine activity, can reduce the skin response and make the test difficult or impossible to interpret.

• I report antihistamines, including those contained in some medicines for colds, sleep or itching.
• I report treatments applied to the skin and any regular or occasional treatment that may alter skin reactivity.
• I also report certain psychotropic medicines or other treatments with antihistamine activity.
• I do not stop my maintenance asthma treatment or reliever inhaler without medical instructions.

I do not cancel the appointment myself. I contact the centre if possible or mention it as soon as I arrive. The team will decide whether the test can proceed, be adapted or be postponed.

• I am pregnant or may be pregnant;
• my asthma is unstable or has recently worsened;
• I have a major eczema flare-up on areas that may be tested;
• I have an infection, fever or an unusual change in my general health;
• I recently had a significant allergic reaction;
• I do not know whether one of my treatments may affect the result or the instructions are unclear.

The day before

• Unless given specific instructions, I can usually eat and drink normally.

On the day of the test

• I wear clothing that makes it easy to expose my forearms or back.
• I do not apply cream, oil or body lotion to the area that may be tested, unless told otherwise.
• I allow enough time for the test and its reading; the total time at the centre may be longer than the skin prick test itself.

Always useful

• the letter from the GP or specialist requesting the consultation, if I have one;
• my prescriptions and an exact list of my treatments, including those taken occasionally;
• relevant letters, laboratory results, previous tests and reports;
• any photographs of the reaction;
• as much detail as possible about the reaction: date, suspected exposure, delay before the first symptoms, type and duration of symptoms, treatments received and outcome.

Only if the team asked me

• the suspected medicine or personal product, in its original packaging;
• a food with its packaging and ingredients; the team will specify whether it needs a particular form, for example fresh, frozen, raw or cooked.

A skin prick test looks for immediate sensitisation to one or more allergens selected from your clinical history. It can contribute to the assessment of different allergies, particularly respiratory or food allergies, and in some specialist contexts to other investigations.

A drop of product is placed on the skin, usually on the forearm or back, then the skin is pricked very superficially through the drop. Positive and negative controls confirm that the test can be interpreted.

Skin prick tests can be performed at any age when clinically indicated. Skin reactivity varies between people and may be lower, particularly in very young children or older people; controls are therefore essential.

Depending on the clinical question: standardised allergen extracts, certain foods or other native products, and sometimes products used in a specialist setting. The allergist selects the relevant tests; there is no benefit in testing everything without a link to your history.

1. Before starting - The professional checks your history, treatments, health and whether instructions were followed. They select the relevant allergens.
2. Applying the drops - Small drops are placed on clean skin on the forearm or back. Their positions are marked.
3. Superficial prick - A small lancet passes through each drop into the very superficial layers of the skin. This is brief, causes little pain and does not usually cause bleeding.
4. Waiting period - You wait without scratching, rubbing or wiping the area. A small weal, redness or itching may appear.
5. Reading - After about 15 to 20 minutes, the professional measures the reactions and checks the controls.
6. Interpretation - The allergist compares the results with your clinical history and decides whether further investigations are needed.

Reactions are usually local and temporary. Generalised reactions are rare. When the history suggests a severe reaction or certain products are tested, the team adapts the precautions.

The result can only be interpreted if the controls are valid. Positivity is defined according to the protocol used and is always interpreted in comparison with the controls and your clinical history.

A positive result is consistent with IgE sensitisation to the tested allergen. It does not necessarily mean that the allergen causes your symptoms.

Conversely, a negative test does not always rule out an allergy. Age, certain medicines, skin condition, timing of the assessment and the nature of the allergen may affect the result.

You can usually resume your normal activities after the test, unless told otherwise.

I ask the team:

• when to restart a medicine that was stopped;
• how to relieve persistent itching;
• how and when the results will be explained to me;
• whether further investigations are needed.

• I have reread the centre's instructions.
• I have checked my medicines with a professional or against the instructions received.
• I have not stopped any treatment on my own initiative.
• My asthma is stable, or I have informed the centre.
• I have not applied cream to the area to be tested, unless told otherwise.
• I bring my treatments, prescriptions and relevant documents.
• I only bring a personal product if I have been asked to do so.
• I have checked the time and the different stages of my appointment.

• A skin prick test is a quick investigation for immediate sensitisation.
• Instructions about medicines are personalised: I never decide to stop a treatment on my own.
• The result only makes sense alongside my clinical history and the allergist's interpretation.

‘Preparing for allergy tests’: a general sheet explaining what to bring and how to prepare when one or more tests are planned.