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Allergy or allergic reactions are hypersensitivity reactions of the immune system of our body to relatively harmless substances, that come into contact usually by breathing, by touch and/or by ingestion. The immune system produces chemical substances (Histamine) and antibodies in response to these substances, known as allergens. The allergen may be a completely harmless substance, like pollen, pet dander etc which may not elicit any reaction in other humans. The severity of the reaction varies from person to person and can be as mild as a minor irritation to as severe as an anaphylactic reaction.

Depending on the route of entry of the allergen, the reaction elicited can vary. Allergic rhinitis (allergen enters through the airway) can cause sneezing, itching of nose/ eyes, runny nose, redness of the eyes, wheezing, cough etc. A food allergy (allergen enters through digestive tract) can cause swelling of lips/tongue, tingling in the mouth, hives, anaphylaxis etc. Insect bites may result in local redness, swelling and other localised/systemic reactions in the body. Similarly, a drug allergy may cause skin rashes in the form of red patches, blebs etc. Atopic dermatitis (skin allergy) can result in redness, itchy flaking/peeling of skin. A severe form of allergic reaction called anaphylaxis can occur leading to loss of consciousness, shortness of breath, drop in BP, nausea & vomiting, weak pulse etc.

Any allergic symptom should be evaluated by a healthcare provider. Based on the clinical history provided and the physical examination, the doctor may advise for a few tests to check if indeed one has allergic symptoms to some allergen.

Allergy Skin Tests – An allergen may be introduced to the patient by a small prick, thereby checking if the body reacts to that allergen. Minute amounts of suspected allergens or their extracts (like pollen/grass, peanut extract, mite proteins) are introduced to the skin and are marked with pen or dye . A small plastic/ metal device is used to prick the skin. Sometimes, the allergens are injected intradermally into the patient's skin, with a needle and syringe, commonly on the inside forearm and the back. There are skin patches available which have the same principle. Local skin reaction to an allergen or protein, proves that one may be allergic to that substance. Although further tests may be required to confirm the same.

Allergy Blood Tests – Detection of specific Immunoglobulin E (IgE antibodies are produced against the allergen) by RAST (Radio Allergo Sorbent Test) or ImmunoCAP tests are performed on blood samples. Raised Total IgE in the serum also points towards presence of some ongoing allergic reaction. There are test panels with multiple common airborne, foodborne allergens to test if the blood sample has specific IgE towards an allergen. These screening panels helps if the patient is unaware of the allergy causing agent.

While avoidance of the allergic substance is the mainstay of treatment of allergic reactions, there are other medications and immunotherapies to overcome the allergy. Allergy tests help us to identify the reaction causing allergen and thereby lead a disease-free life.

Dr. Adithya S

Consultant Pathologist
MD Pathology