Omalizumab (brand name Xolair^®) is a recombinant DNA-derived humanized IgG1 kappa monoclonal antibody used in the treatment of patients with moderate or severe asthma who have demonstrated a positive allergy skin test and whose symptoms are not controlled by inhaled corticosteroids.Allergic asthma is mediated by IgE released by B cells in response to allergen. Circulating IgE binds to the high-affinity IgE Fc receptor (FcεRI) expressed on basophils and mast cells, triggering the release of histamine, leukotrienes and other mediators associated with the pathophysiology of asthma. Omalizumab is directed against the Fc region of human immunoglobulin E (IgE). By binding to circulating IgE at the site of FcεRI binding, this therapeutic antibody prevents the interaction of IgE with its receptor thus limiting mediator release. Treatment with omalizumab has also been demonstrated to reduce the expression of FcεRI on mast cells and basophils, providing additional clinical benefit.Human anti omalizumab, clone AbD20669 is a paratope specific anti-idiotypic (Type 1) antibody that binds specifically to omalizumab but not to free IgE or the drug/immunoglobulin complex. This antibody can be used to measure omalizumab levels in serum from patients. Clone AbD20669 is particularly suited for use as a capture reagent in Pharmacokinetic (PK) assay development.Other Type 1 (HCA235) and Type 3 (HCA237, HCA238) antibodies to omalizumab are also available from Bio-Rad in IgG1 and Fab formats. This range of anti omalizumab antibodies forms part of a wider and expanding portfolio of anti-idiotypic antibodies that have been developed for the detection of biotherapeutics.