Allergy Diagnosis
The diagnosis of allergy is dependent on the identification of a specific IgE antibody against the item. With the expert allergist opinion, this is the most important step in confirming the diagnosis. Different tests have different advantages and disadvantages regarding accuracy, ease of use, reproducibility and cost. The skin prick test is the most sensitive test. It provides rapid results within 20 minutes. However, sometimes it cannot be done because the patient has severe skin problems, dermatographism, or because the patient is taking drugs that may affect the test, such as anti-histamines. That’s when the blood IgE test can be useful.
I. Allergy Skin Test
The Skin Prick Test is a common method of finding out whether a person is allergic to various allergens. It is economical and results are immediate.
The idea is to introduce small standardised quantities of different known allergens to the patient’s skin (usually arm or back). Any swelling indicates an allergy to the substance – the bigger the swell, the more allergic the person is to the substance.
Positive and negative controls (glycerinated histamine and placebo respectively) will also be administered. This removes false-negatives (no reaction to allergens due to the presence of anti-histamines) and false-positives (reacting to allergens but no allergy condition).
Results will be evident in 15 to 20 minutes when the doctor or nurse will record the wheal (swelling and edema) and erythema (flame / redness). The results will determine the patient’s degree of allergy to each substance.
Once the patient knows exactly what he is allergic to, he can take steps to avoid contact with those substances or receive allergen specific immunotherapy treatment for inhalant items.
II. Serum IgE Test
A blood sample is required from the patient. It can be a small drop of blood through a finger prick or a larger amount through venous sampling. There are different methods of measurement. It can be qualitative or quantitative. The standard reference test is ImmunoCAP. Immunoblotting, Lateral flow assay and ELISA are different modalities of measurement. Each has its advantages regarding specificity and sensitivity as well as cost. Usually, the test is more expensive than the skin prick test and it takes longer to get the results.