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How does Xolair affect IgA and IgE levels?

Medically reviewed by Kristianne Hannemann, PharmD. Last updated on April 30, 2025.

Official answer

by Drugs.com

Xolair (a medicine also called omalizumab) is used to treat allergic asthma, nasal polyps and hives. It may also be used for people with food allergies. It targets a specific part of your immune system called immunoglobulin E (IgE), but research shows that Xolair does not affect IgA levels.

What Does Xolair Do?

Xolair works by blocking IgE, a type of antibody (a tiny protein in your blood) that causes allergic reactions. Here’s how:

  • It grabs onto free-floating IgE in your blood, like a key fitting into a lock.
  • It stops IgE from attaching to cells that release chemicals (like histamine) that cause allergy symptoms.
  • It reduces the number of “allergy sensors” (called IgE receptors) on your cells over time, making you less reactive to allergens.

Does Xolair increase or decrease IgE levels?

Xolair decreases free IgE levels in the blood within 1 hour after the first dose. The average reduction observed in studies was more than 96%. However, total IgE levels in the blood increase after the first dose because once they are attached to Xolair they clear more slowly from the body.

Even though IgE levels appear higher, the binding of Xolair to free IgE reduces the amount of free IgE available to trigger allergic reactions. After stopping Xolair, your total IgE might stay high for up to a year because these “clumps” take time to clear out of your system.

Related questions

Does Xolair Affect Other Parts of Your Immune System?

Xolair is very specific, and doesn’t appear to affect other immunoglobulins:

  • IgA, IgG, IgM: These are other types of antibodies that fight infections. Studies show Xolair doesn’t change their levels.
  • Even if someone has low IgA (a common immune issue), Xolair won’t make it worse.

Conclusion

Xolair demonstrates a highly selective effect on immunoglobulin levels in the body, with significant impacts on IgE but no meaningful effect on IgA or other immunoglobulin classes. This selective action is central to omalizumab's therapeutic value in treating IgE-mediated allergic conditions while minimizing broader immune system disruption.

Xolair dramatically reduces free IgE levels while paradoxically increasing total IgE measurements due to the formation of longer-lasting omalizumab-IgE complexes.

References
  1. Çildağ, S., et. al. 2018. The effect of omalizumab treatment on IgE and other immunoglobulin levels in patients with chronic spontaneous urticaria and its association with treatment response. Postepy dermatologii i alergologii, 35(5), 516–519. https://doi.org/10.5114/ada.2017.71422
  2. Xolair [package insert]. Updated 2024. Genentech, Inc. Accessed April 30, 2025 at https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7f6a2191-adfb-48b9-9bfa-0d9920479f0d

Read next

How long before Xolair starts working?

Free serum IgE levels are decreased within an hour of Xolair administration. However it may take several months for the full effects of Xolair to be seen, although some symptom improvement may be noted after a few weeks. Significant improvements were noted after 4 months in those with allergic asthma, after 3 months in those with chronic urticaria, and after 16 to 20 weeks in those with Ig-E-mediated food allergies. Continue reading

Does Xolair cause hair loss?

Hair loss (alopecia), has been reported in Xolair clinical studies in at least 2% of people with chronic hives. Hair loss has also been noted in several case reports with Xolair. The hair loss effect appears to be transient, lasting from 3 to 4 months. Due to limited data, the exact cause of hair loss or how often it occurs is not known. Continue reading

Does Xolair cause cancer?

Xolair is associated with a slightly higher risk of cancer, but cancer specialists have determined that this does not mean that Xolair causes cancer. Research has shown that cancer occurred in 20 out of 4127 trial participants (0.5% of Xolair-treated study volunteers) and 5 out of 2236 (0.2%) of people who were assigned an inactive treatment. Continue reading

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