How to Diagnose Allergies

Various methods are used in diagnosing and assessing allergies. One is a skin test, the simplest way of diagnosing allergies. Allergy skin testing is a safe and simple method that can be useful in identifying allergic sensitivities. It is also known as a skin prick test or prick testing. It is done by pricking the skin and introducing suspected allergens into it to check if a reaction occurs. The skin is punctured using a lancet, then a minute amount of suspected allergens and/or their extracts are either introduced intradermally or into scratchings made on the individual's skin. Testing is usually done on the inside of the forearm and back. If allergic to the substance, the skin will develop a visible inflammatory reaction ranging from reddening of the skin to full-blown hives, itching or raised bumps or welts. The reaction usually occurs in half an hour.

Skin testing can be used to confirm if symptoms like sneezing, skin rashes and wheezing are caused by allergies. This method can also be helpful in distinguishing substances that cause allergies. The skin testing method is widely used in diagnosing allergic conditions like hay fever, allergic asthma and dermatitis (eczema). It's safe for all people, including infants and older adults.

Though the skin prick test may be the most preferred method, sometimes it's not recommended. Skin testing may not be advised if an individual is taking medications like antihistamines, antidepressants and some heartburn medications. These medicines interfere with the skin test results. Skin testing is also not recommended for those who have severe skin diseases like eczema or psoriasis that affect large areas on the arms and back where testing is usually done. Individuals who are highly sensitive to suspected allergens may also not be allowed to undergo skin tests. Anaphylaxis, a severe allergic reaction, could be triggered.

Some people may have a delayed-type hypersensitivity (DTH) reaction, which are from IgE antibodies. Called Arthus reactions, they can occur 6 hours after application of the allergen and last up to 72 hours. They are fairly common and usually are easily treated with anti-inflammatory creams.

Blood testing is another way to diagnose allergies. It is a diagnostic method used in determining the level of IgE antibodies present in a person with allergic reactions and symptoms. The most commonly used blood test is called RAST (radioallergosorbent test). It may be used even when the patient is under medication for allergies, or if the patient has eczema. In this procedure, blood is drawn from a vein and tested for presence of allergen-specific antibodies. This method is complementary to skin testing since they allow to corroborate and measure the level of sensitization. A sample of 2-3 cc of blood is enough to distinguish an individual's state of being sensitive to a dozen different allergens. A thorough history is taken together with the procedure since there is a possibility of a positive blood test without symptoms. Because of this, the diagnosis will be made on the basis of the information gathered.