What is a prick test?
The prick test is a frequently used skin test in allergy diagnostics. It can be used to find out whether someone is allergic to certain substances (for example pollen). Since the prick test is performed directly on the skin of the person concerned, it belongs to the in vivo tests (= “on the living object”). In contrast, a laboratory test using a blood sample is referred to as an in vitro test (= “in a glass”).
When is a prick test performed?
Doctors use the prick test when they suspect an allergy to the following substances:
- Pollen (e.g. from birch, alder, hazelnut and grasses)
- House dust mites
- Molds
- Animal hair
- Food (milk, egg and fish protein as well as legumes and fruits)
- Insect venoms
So-called type I allergies can be detected with the prick test. In this type of allergy, those affected react within seconds to minutes to the allergy trigger (allergen). In rare cases, delayed reactions are also possible. You can read more about this on our overview page on allergies.
What is done in a prick test?
For the prick test, the doctor drips standardized, industrially produced allergen solutions onto the inside of the patient’s forearm. Using a special lancet or prick needle, he then pricks the skin superficially through the drop (only lightly – it should not bleed).
For each prick test, an aqueous solution and a solution with histamine are also applied. The first must not trigger a reaction, the second must.
After about 15 to 20 minutes, the doctor examines the tested skin sites. If the patient reacts allergically to a substance, the skin at the corresponding site becomes red, itchy and a wheal forms.
Affected individuals continue to be monitored immediately after the test (for at least 30 minutes after the allergen is introduced). This allows medical staff to intervene immediately should the person have a severe reaction to the allergen.
What are the risks of a prick test?
Even small amounts of the allergen can, in rare cases, cause symptoms such as shortness of breath, dizziness, vomiting and a drop in blood pressure. In extreme cases, allergic shock (anaphylactic shock) with cardiac and circulatory arrest can occur. If a patient has had a life-threatening reaction to an allergen in the past, this must also not be tested with a prick test.
If affected individuals are known to have other serious allergies, they are usually monitored for several hours after a prick test. Occasionally, the allergic reaction occurs with a delay, and thus quick action can be taken in an emergency.
When not to perform a prick test?
What do I have to observe after a prick test?
After a prick test, you should continue to observe the tested skin sites over the next few hours. In a few cases, the reaction is delayed. Under certain circumstances, further symptoms may develop after a few hours (two-pointed course). Inform your doctor about such delayed reactions.
If you suddenly experience symptoms such as dizziness, shortness of breath or abdominal cramps after the prick test, dial 911 immediately.
Overall, the prick test is a quick, simple and relatively safe method for allergy diagnosis and has become the standard method.
However, the test results can only be used in conjunction with a detailed discussion of the reactions observed by the patient himself (anamnesis). Positive reactions in the prick test are not necessarily synonymous with an allergy to the substance in question.
