Allergy | Immunoglobulin E (IgE)

Immunoglobulin E (IgE) is one of the five classes of antibodies (immunoglobulins) produced by the human immune system, alongside IgG, IgM, IgA, and IgD. It¡¯s a specialized antibody best known for its central role in allergic reactions and defense against certain parasitic infections. Though it¡¯s present in very low amounts in the blood¡ªmaking up less than 0.05% of total immunoglobulins¡ªIgE punches above its weight in specific immune responses. IgE plays a central role in allergic diseases such as asthma, hay fever (allergic rhinitis), food allergies, and atopic dermatitis. 

1. Total IgE Testing: Measures the overall concentration of IgE in the blood (in units like IU/mL or kU/L). It provides a general indicator of allergic or atopic tendency but doesn¡¯t specify triggers.
2. Allergen-Specific IgE Testing: Identifies and quantifies IgE antibodies directed against particular allergens (e.g., pollen, peanuts, pet dander). This is typically done using techniques like nephelometry, ImmunoCAP (a fluorescence enzyme immunoassay), or other immunoassays.

An IgE blood test measures the levels of total IgE (general amount in the blood) or allergen-specific IgE (directed at particular allergens like pollen, foods, or dust mites). Elevated levels of allergen-specific IgE indicate sensitization, meaning the immune system has developed an allergic response to that substance.
Conditions Diagnosed: It¡¯s used to confirm allergies in conditions such as: