A nurse in an allergy clinic is caring for a client who has a history of seasonal allergy symptoms. The client had a radioallergosorbent test (RAST) completed on a previous visit. The nurse should recognize that an elevation in which of the following immunoglobulins indicates a positive result?

Choice A rationale Immunoglobulin G (IgG) is the most abundant class of antibody found in human plasma, accounting for about 75. Choice B rationale Immunoglobulin A (IgA) is a secretory antibody critical for mucosal immunity, primarily found in tears, saliva, breast milk, and secretions of the respiratory, gastrointestinal, and genitourinary tracts. It prevents pathogen colonization of mucous surfaces. Normal serum IgA ranges are approximately 70 to 400 mg/dL. An elevation in serum IgA does not directly indicate a positive RAST result for a seasonal allergy. Choice C rationale Immunoglobulin M (IgM) is the first antibody produced in response to an initial antigen exposure, providing short-term primary defense and efficient complement activation. It is primarily found in the blood and lymph fluid. Normal serum IgM ranges are approximately 40 to 230 mg/dL. Elevated levels signify recent infection but are not the specific marker used to determine a positive RAST result for hypersensitivity. Choice D rationale Immunoglobulin E (IgE) is the antibody class responsible for immediate Type I hypersensitivity reactions, including seasonal allergies, asthma, and anaphylaxis. The RAST test specifically measures circulating antigen-specific IgE antibodies bound to the allergen. Normal serum total IgE ranges are generally 0 to 100 IU/mL. An elevation confirms the sensitization to specific allergens, resulting in a positive RAST.