An allergic reaction may occur anywhere in the body, but usually appears in the skin, eyes, lining of the stomach, nose, sinuses, throat and lungs — places where special immune system cells are stationed to fight off invaders that are inhaled, swallowed or come in contact with the skin.
Skin tests, in most situations, are preferable because (1) the results are available immediately, (2) they are less expensive and (3) they are more sensitive to subtle allergies.
A blood test is appropriate in certain situations, particularly when you (1) cannot suspend antihistamine therapy which can inhibit skin tests, (2) have widespread skin disease making skin testing difficult, (3) are so sensitive to the allergen that the test might be risky or (4) cannot be skin tested for some other reason.
Why is it that frequent exposure to an allergen can increase sensitivity and cause allergic reaction, yet repeated exposure to an allergen in allergy shots helps build ups immunity? Regularly scheduled, repeated exposure to small amounts of an allergen can lead to immunity, whereas infrequent and erratic exposure does not confer immunity but increases the likelihood of producing allergen sensitization.
Irregular exposure to allergens can lead to the production of antibodies (called IgE-mediated antibodies). The presence of these antibodies, when exposed to an allergen can lead to an allergic reaction.
In allergy shots or immunotherapy, the allergen exposure is closely regulated and given on a scheduled basis. Small amounts of allergens are given over a period of time to build up to maintenance doses. This leads to the production of blocking antibodies (called IgG antibodies) and a decrease in the level of allergic or IgE-mediated antibodies.
The problem is an oversensitivity of the lungs and airways, which overreact to certain “triggers” and become inflamed and clogged.
To diagnose asthma and distinguish it from other lung disorders, physicians rely on a combination of medical history, a thorough physical examination, and certain laboratory tests. These tests include spirometry (using an instrument that measure the air taken into and out of the lungs), peak flow monitoring (another measure of lung function), chest X-rays and sometimes blood and allergy tests.
These problems occur because the airways of the lungs are getting narrower. The muscles that surround the airways tighten, the inner lining of the airways swells and pushes inward, and the membranes that line the airways secrete extra mucus, which can form plugs that further block the air passages. The rush of air through the narrowed airways produces the wheezing sounds that are typical of asthma.