The “Prick Test” - Welcome to the Allergy Club!
Sensitization to allergens
A runny nose, itchy eyes, relentless cough or skin rash are all indications of an allergy and require medical attention. The task of a dermatologist, or allergy specialist, is to identify the triggers of allergies. The skin prick test is the standard test used to determine whether there are certain allergens a patient has become sensitized to.
Rules for performing the “prick test”
An article in “Medical Tribune” sets out the ten steps used in performing the prick test in order to make a successful allergy diagnosis. Here is an abridged version of the article:
Discontinue the use of antihistamines
Document the patient history
Clean the patient’s forearm with disinfectant
Label the arm with a ballpoint pen: one number per allergen
Apply the allergens, saline (as negative control) and histamine (as positive control)
Pierce each drop with a scalpel to a depth of 1 mm into the skin
Wipe away the remaining drops
Read the test after 15 minutes by noting the size of any wheals that have formed
Calculate the skin index (see below)
Disinfect the patient’s skin.
The skin index is a measure of the sensitivity of the body to an allergen.
What happened?
A minimum of ten allergens have been introduced into the body. Some of these the patient probably was not previously allergic to but it is possible that an allergy to these substances may now develop, even if all the results were negative. Welcome to the club of allergy sufferers!
You have just been sensitized!
In a similar way to a bee sting, different substances, in this case various allergens, have been introduced into the body through the skin. The body may now have become sensitized to these allergens. By definition, the sensitization of the body occurs when there is an initial contact with a foreign substance or an allergen, which then results in the development of a specific immune response.
What happened exactly?
Allergens, which do not normally pass through the skin, have been introduced into the body provoking a response from the immune system. If the allergen dose was low enough in the test, the second barrier of the immune system (T cells and macrophages) will take control and destroy the foreign substance. However, if the allergen dose is higher and the T cells and macrophages are not able to fight the allergen, the body will develop IgE antibodies against the invaders due to the activation of the third barrier of the immune system. It takes several days for the IgE antibodies to be produced and the patient remains completely unaware of what is happening in their body until the allergen is encountered for a second time – this is when an allergy becomes apparent with the symptoms associated with that specific allergen.
The basic rule for allergy testing
Ask your doctor to perform only a radioallergosorbent test (RAST) or one of the other newer methods of allergy testing. The RAST test investigates whether there are antibodies to particular allergens present in the blood.
Note: allergy testing should be performed only ex vivo (outside the body), never in vivo (in the body).
