Skin prick testing is a form of allergy test in which skin is pricked with the tip of a lancet through a tiny drop of allergen solution. Lancet tip feels sharp but not usually painful. These tests can be carried out on all age groups including babies. Before these tests can be done the patient needs to avoid taking any antihistamines or cough syrups etc. that contain antihistamines for at least 72 hours. Antihistamine medications interfere with the test and may make a test falsely negative.
Skin prick testing is a simple and a quick procedure. It is safe in the hands of a trained person. Most reactions are local but rarely a general reaction can occur that a trained person can manage. Skin prick testing is usually done on the inner forearm but any other part of the body i.e. thigh or back may be used. In patients with wide spread eczema a clear patch of the skin has to be found. A careful detailed history is taken and a list is made of the allergens selected. One can use commercially prepared allergens or fresh foods. To insure the skin response is a true reaction, positive and negative controls are done with histamine and normal saline water. The result of the testing is read in 10-20 minutes. The skin may become itchy and within a few moments show a palpable wheal like a nettle sting. Reactions of 3mm or more are significant of allergy though a larger size increases the predictability of the positive allergy.