Test Catalog

Test ID: IL5P    
Interleukin 5, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluation of patients with disorders known to be associated with hypereosinophilia

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Interleukin-5 (IL-5) is a homodimer composed of two 20-kD subunits.(1) It is expressed primarily by CD4+ Th2 (helper T cells, subset 2) cells and, to a lesser extent, by activated mast cells.(2) IL-5 acts on mature eosinophils, leading to proliferation, activation, and differentiation. IL-5 is a critical part of the immune response to helminths. Eosinophils activated by IL-5 will bind, through Fc receptors, to helminths that have been opsonized by IgG or IgA.


Elevations in IL-5 may be observed in conditions associated with hypereosinophilia. Hypereosinophilia is most commonly seen in various forms of atopic disease, including urticaria, asthma, allergic bronchopulmonary aspergillosis, and drug allergies.(3) Elevated numbers of eosinophils may also be observed in certain vasculitides, specifically eosinophilic granulomatosis with polyangiitis (EGPA). EGPA is characterized by asthma, pulmonary infiltrates, history of allergies, and hypereosinophilia usually above 1500/mL. Hypereosinophilia may also be observed in certain primary immunodeficiencies (such as Job syndrome), leukemias, and lymphomas. IL-5 is thought be important in driving eosinophil proliferation in these various conditions.(4) Recently, an advisory committee of the FDA has recommended that mepolizumab, a monoclonal anti-IL-5 antibody, be approved for the treatment of severe eosinophilic asthma in adults.(5) Other IL-5 blocking antibodies (reslizumab and benralizumab) are also in development, with clinical trials designed to determine specific clinical utility.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

< or =1.0 pg/mL

Interpretation Provides information to assist in interpretation of the test results

Elevated concentrations of interleukin-5 (IL-5) may indicate an expanded Th2 (helper T cells, subset 2)-immune response, which may be associated with hypereosinophilia.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Interleukin-5 (IL-5) is a nonspecific marker associated with a Th2 (helper T cells, subset 2)-immune response, and is not diagnostic for any specific disease or disease process. Elevated concentrations of IL-5 must be interpreted within the clinical context of the patient.


Normal concentrations of IL-5 do not exclude the possibility of a Th2-immune response or hypereosinophilia.


IL-5 has limited stability. Following centrifugation, plasma must be either immediately frozen or refrigerated. Samples can only be stored at refrigerated temperatures for 24 hours, after which time samples must be frozen. Storage of plasma for any length of time at room temperature is not acceptable.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Kouro T and Takatsu K: IL-5 and eosinophil-mediated inflammation: from discovery to therapy. Int Immunol 2009;21:1303-1309

2. Kusano S, Kukimoto-Niino M, Hino N, et al: Structural basis of interleukin-5 dimer recognition by its alph receptor. Protein Sci 2012;21:850-864

3. Joseph J, Benedict S, Safa W, et al: Serum interleukin-5 levels are elevated in mild and moderate persistent asthma irrespective of regular inhaled glucocorticoid therapy. BMC Pulm Med 2004;4:2

4. Corren J: Anti-interleukin-5 antibody therapy in asthma and allergies. Curr Opin Allergy Clin Immunol 2011;11:565-570

5. Sutton SA, Assa'ad AH, Rothenberg ME: Anti-IL-5 and hypereosinophilic syndromes. Clin Immunol 2005;115:51-60