Allergy tests

There are two types of tests to find out if a child is allergic:

• Skin prick tests è The skin is punctured with a small lancet through a drop of the suspect allergen. A minute amount of allergen gets into the skin, to see if a reaction occurs. After 15-20 minutes, the presence of a wheal lets know which allergens the patient is sensitized to.

• Blood tests è They are complementary to skin tests. They allow to confirm and to quantify the degree of sensitization. A sample of 2-3 cc of blood is enough to study sensitization to a dozen of different allergens.

The Phadiatop® test is a blood qualitative test for the presence of sensitization: a positive result means that the patient will most probably be allergic, while a negative test means the patient will most probably not be allergic. This test is used as a screening method for allergy.

It has been estimated that a person will come in contact during lifetime with thousands of substances capable of inducing allergy.

Fortunately, only a few of them will cause problems. Finding the cause of allergy is sometimes a very difficult task, and the number of tests to be performed for a patient is limited, specially in children. People usually become allergic to substances they have a close and frequent contact with: the more frequent and more intense a contact with a substance, the more probable that one becomes allergic to it. Therefore, the tests to be performed must be based on a detailed medical record, to select the allergens which more probably are involved. For instance, a child with conjunctivitis when near a cat, will probably be sensitized to cat dander. When symptoms appear in Spring, in the countryside, pollen allergy is probable. The specialist must know what are the most relevant plants, molds or mites in the area. Sensitization to pollen of olive tree is very common in the Mediterranean area, while allergy to birch pollen is exceptional. The opposite happens in North Europe countries. House dust mites species may vary according to climate conditions.
On the other side, it is essential to make a correct interpretation of results of tests. Not seldom, a patient may have positive results in tests against some allergens that are not clinically relevant, that is, allergens which are not responsible for triggering symptoms in that patient.
It is important to realize that sometimes symptoms appear when there is a time coincidence of several factors which would not be able to induce those symptoms separately (an amount of allergens together with a viral infection, or exercise, or cigarette smoke, cold air, pollution,…).
This means that the physician who performs, reads and interprets these tests must be a skilled specialist, with the necessary experience and training to reach a accurate diagnosis.