Omalizumab (Xolair®) - Therapeutic Drug Monitoring (TDM)

Omalizumab is a humanised monoclonal antibody that selectively binds to human immunoglobulin E (IgE), manufactured by recombinant DNA technology in a Chinese hamster ovary cells. Omalizumab prevents binding of IgE to FceRI (high-affinity IgE receptor), thereby reducing the amount of free IgE that is available to trigger the allergic cascade. Treatment of atopic subjects with omalizumab resulted in a marked down-regulation of FceRI receptors on basophils.

Clinical Use

In Europe, omalizumab is indicated for treatment of improve the control of severe persistent asthma that is caused by an allergy (IgE-mediated). It is used as an add-on to existing asthma treatment in patients of at least six years old.

Moreover, omalizumab is used to treat chronic (long-term) spontaneous urticaria (itchy rash), as an add-on to existing treatment in patients aged 12 years or over who do not respond to treatment with antihistamines.

Testing omalizumab concentration:

The assay is performed using Enzyme Linked Immunosorbent Assay (ELISA). The limit of quantification (LOQ) for omalizumab in serum is 0.01 µg/mL.

Testing omalizumab anti-drug antibodies (ADA):

The assay is performed using radioimmunoassay (RIA). The limit of quantification (LOQ) for ADA is 12 AU/mL.

Clinical Relevance

No response or loss of response of treatment with omalizumab.

During treatment, some patients may develop antibodies to omalizumab; anti-drug antibodies (ADA).

With level testing of biologics, efficacy of therapy can be improved, as treatment decisions may need to be adapted depending on the test results in conjunction with clinical responses to treatment.

Data and interpretation of omalizumab ADA and its serum levels are still very limited.

Personalized Medicine

Monitoring biologic levels in individual patients allows optimization of treatment efficacy by adjusting therapy depending on the specific response of the patient. When drug levels are decreased in a non-responder, this may reflect formation of inactivating antibodies directed to the biologic treatment. Immunogenicity testing identifies presence or absence of inactivating antibodies, which guides the next treatment decision – switch to other biological treatment, lowering of dose or intensify dosing. Reducing drug dosage in well-responding patients with relatively high drug levels cuts down cost. A personalized approach can improve therapy efficacy and quality of life.

Read more on the following pages:

Order of test: Print and complete the request form and send it together with the sample.

For further questions please contact us.

To receive more information about drug monitoring please visit

20 years experience