There are several methods for the diagnosis and assessment of allergies.
Besides a thorough medical history, the doctor will perform a number of skin tests and/or a blood test called radioallergosorbent test (RAST).
The typical and most simple method of diagnosis and monitoring of Type I Hypersensitivity is by skin testing, also known as prick testing due to the series of pricks made into the patient's skin. Small amounts of suspected allergens and/or their extracts (pollen, grass, mite proteins, peanut extract, etc.) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). The allergens are either injected intradermally or into small scratchings made into the patient's skin, often with a lancet. Common areas for testing include the inside forearm and back. If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to full-blown hives in extremely sensitive patients.
After performing the skin test and receiving results, the doctor may apply a steroid cream to the test area to reduce discomfort (such as itching and inflammation).
While the skin test is probably the most preferred means of testing because of its simplicity and economics, it is not without complications. Some people may display a delayed-type hypersensitivity (DTH) reaction which can occur as far as 6 hours after application of the allergen and last up to 24 hours. This can also cause serious long-lasting tissue damage to the affected area. These types of serious reactions are quite rare.
Additionally, the application of previously unencountered allergens can actually sensitize certain individuals to the allergen, causing the inception of a new allergy in susceptible individuals.
Skins tests also are not always able to pinpoint a patient's specific allergies if the patient has an allergy but does not react to the skin test allergen.
Another method used to qualify type I hypersensitivity is measuring the amount of serum IgE contained within the patient's serum. This can be determined through the use of radiometric and colormetric immunoassays. Even the levels the amount of IgE specific to certain allergens can be measured through use of the radioallergosorbent test (RAST).