Allergies and the benefits of serum testing
The best definition of an allergy is: “a classic overreaction by the immune system to an otherwise harmless substance”. Pollen from Bermuda grass, for example, is typically harmless, but in atopic patients, the immune system may identify it as harmful. This sets off a cascade of events in the immune system resulting in the increased production of allergen-specific IgE.
Like all antibody isotypes, IgE is composed of two fragments: Fab and Fc. The Fab fragment has a high affinity to the allergen against which it was produced, while the Fc fragment has a high affinity to specific receptors on the surface of mast cells. IgE bound to mast cells via the Fc fragment can bind its specific allergen via the Fab fragment, resulting in the release of histamine, bradykinin, serine proteases and other factors that result in an onset of symptoms (Figure 1).
There are two methods of identifying allergens that are causing symptoms – intradermal and serum allergy tests.
1. Intradermal testing involves introducing a small amount of a specific allergen into the patient’s skin and observing whether or not a reaction occurs.
2. Serum allergy testing involves quantifying the amount of IgE in serum that specifically recognizes an allergen of interest.
Both methods have their merits, but this article will summarize the benefits of serum testing.
The goal of serum allergy testing is to measure the amount of allergen specific IgE in the serum. Individual allergens are coated onto the bottom of a 96-well dish and the serum exposed to each individual allergen. An ELISA assay is performed, allowing for the quantification of IgE antibody specific to a particular allergen. Allergens that bind large amounts of IgE are considered the most allergenic. Due to the relatively low abundance of serum IgE and interference from other antibody isotypes, especially IgG, standard ELISA assays are subject to dramatic false negatives.
The SPOT Platinum assay improves on the standard ELISA. It optimizes the coating of allergen to the plate by retaining the three-dimensional structure of the allergen for maximum antibody binding. Concurrently, blocking the allergen plates has been improved by reducing the binding sites for all antibody isotypes other than IgE. These two steps increase the specificity and sensitivity of the test to more than 97%. Add to this the modifications in reagents at other steps in the assay, and you have a test that not only answers past criticisms but surpasses them.
While food allergy testing has had its share of criticism, studies have shown a 53% decrease in symptoms simply by introducing a diet change based on testing results. When combined with hyposensitization to inhalant allergens, improvement rates can exceed 85%.