Allergy laboratory

Specific IgE measurement

Summary

Science

Clinical

Science

An allergic reaction is initiated when IgE antibodies encounter ‘harmless’ environmental molecules called allergens for which they have a single specific affinity. These IgE antibodies are concentrated on mast cells. When they are cross-bridged by the allergen the mast cell releases chemicals that generate the allergic symptoms. The laboratory test to detect what specific substances cause allergies doesn’t measure the outcome of a controlled allergic response as exposure tests do but instead measures the amount of specific IgE with affinities for known allergens. Patient serum that has been separated from clotted red blood cells is added to a cellulose polymer sponge that has been impregnated with either a single or mix of allergens. Any IgE present, that is specific for the allergens, will bind to them whilst the rest is washed off. Next another enzyme-tagged antibody is added that binds to all IgE. A substrate is then added that reacts with the enzyme producing a colour change that can be quantified and compared with the colour change from reactions with known concentrations of specific IgE to calculate a result for the patient. The calculated quantities of specific IgE are then compared with the amount of specific IgE that people without allergies to the substance in question expect to have.

This test is generally automated with the majority of laboratories using an assay called IMMUNOCAP, which produces accurate standardised results and can identify specific IgE to many different allergens.

• Background
• Clinical