Diagnosis of Allergy

Clinical history.

Intraepidermal test (prick test). It is used to investigate immediate or IgE mediated hypersensitivity. Food allergens, Hymenoptera poisons, inhaled allergens such as dust mites, tree and plant pollen, fungi, animal epithelia, and any other allergen can be studied. It consists of applying a drop of the extract of the allergen to be evaluated on the forearm and the realization of a small puncture with a lancet. In the case that the patient is sensitized (positive test) a small wheal appears (inflammation, redness, and itching) in the puncture area. They are very safe, sensitive and fast tests (20-30 minutes).

Intradermal test. It is used to investigate immediate and also delayed reactions. It is usually used to study medications. It involves injecting a small amount of the allergen into the dermis (similar to a tuberculin test).

Epicutaneous test (patch test). It used to investigate delayed hypersensitivity. It consists of applying on the skin, one or several of the allergens responsible for contact skin reactions. The patch is left on for 48 hours. It can also be performed with drugs.

Blood tests for the study of tryptase (useful during anaphylaxis) and specific IgE (against inhaled allergens and food).

Nasal, conjunctival or bronchial exposure test with an allergen. It is used when we suspect immediate reactions. It consists of applying the allergen inside the nose, eye or bronchus (lung) respectively. It is used to establish what symptoms the allergen produces when breathing or coming into contact with the eyes. It is usually done to confirm which allergen is responsible for the symptoms in a patient who has several positive tests.

Oral exposure with foods tests. The patient has to take, in a controlled way, a portion of food that we suspect could have caused an allergic reaction, for confirmation or discard. Small amounts of food are given, which gradually increase until reaching a normal ration. It is considered a risk test, so it should always be carried out in a hospital with trained personnel to counteract any possible reaction to the food to study. Small amounts of it are given and at each specific time, the quantity is increased until reaching the normal dose of the food.

Test of oral, subcutaneous, intravenous, or intramuscular exposure to drugs. It consists of the patient taking, in a controlled way, a medication that is suspected of causing an allergic reaction. The medication can be taken orally, subcutaneously, intramuscularly or intravenously. Risk tests are considered, so they should always be performed in a hospital with trained personnel to counteract any possible reaction.