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Prick tests

Articles - Allergology

10.11.2021

Prick test is a basic method of diagnosing allergic diseases

The principle of prick-testing is that extracts of various allergens are injected into the patient’s skin (prick in translation from English means “pricks”), and then the body’s reaction to them is recorded.

Indications for pre-test

The prick test is an ideal option for detecting irritants that cause allergic rhinitis, bronchial asthma and food allergies.

Based on the results of the prick test, the doctor makes a decision to carry out specific immunotherapy (SIT) – a series of allergy shots.

Prick tests can give false results if the patient has a reaction to cross-allergens (that is, to allergens similar in structure).

Поширені тригери алергії

Contraindications for conducting a pre-test

The prick test can only be performed on healthy skin.
Dermographism (skin reaction to mechanical irritation).
Fear of needles and injections in children.
Allergy or other chronic diseases in a state of exacerbation.
Pregnancy.
Acute infectious and respiratory diseases.
Mental illnesses.
A severe form of bronchial asthma
Eye inflammation (conjunctivitis).
High temperature.
Anaphylactic reactions to certain allergens (eg, latex).

How the procedure works

The patient’s forearm skin is treated with ethanol. Then, at a distance of 2–3 cm, drops of histamine solutions (positive control), sodium chloride (negative control) and various allergens are applied. These can be extracts of plant pollen allergens, household allergens (dust), food allergens, and animal allergens (wool). There is a standard set of allergens for the test, but the specialist, based on the patient’s symptoms and medical history, can select an individual set of stimuli for him.

A puncture is made through the drops of solutions with a special prick-lancet (the needle length is 1 mm, which makes the procedure painless and bloodless, since the presence of blood at the puncture site can affect the result). A separate sterile prick-lancet is used for each puncture, after which it is considered used and disposed of. Next to the puncture site, the doctor conducting the test can make an inscription with the name of the allergen with a colored marker.

The test results can be seen in 10–15 minutes. A positive reaction to an allergen is considered redness or the presence of a blister measuring 3–7 millimeters in size. A pronounced positive reaction is 8–12 mm in size. And a hyperallergic reaction is 13 mm or more. The calculation is made by the diameter of the largest blister.

During one test, you can check the body’s reaction to 14–16 allergens. Negative results of the prick test almost always mean the absence of an allergy. Although in some cases, false negative results also occur. They show that there is no allergy, although in fact there is. In this case, the doctor may prescribe a repeat test for the patient.

How to prepare for the procedure

10 days before the skin prick test, you should stop taking antihistamines and antidepressants. It is worth telling your doctor about absolutely all the medications you are taking, because some of them need to be stopped a month before the procedure. By the way, antidepressants and corticosteroid ointments also affect the test results.
If you have been vaccinated, at least 3 weeks must have passed since the procedure.
On the day of the procedure, it is forbidden to use cosmetic skin creams in the skin prick test area. Do not use household chemicals (dishwasher, furniture and window cleaners).
Before the procedure, you should go to the toilet, because you will need to sit for about 20 minutes.