Xolair Interferes with Allergy Skin Testing
Yes, Xolair (omalizumab) significantly interferes with allergy skin testing by reducing free IgE levels by 49-98% and decreasing IgE receptor density on mast cells and basophils, which will suppress or eliminate skin test reactivity. 1, 2
Mechanism of Interference
Omalizumab works by binding to circulating IgE and preventing it from attaching to high-affinity IgE receptors (FcεRI) on mast cells and basophils 2, 3. This creates two specific problems for allergy testing:
- Free IgE levels drop dramatically within 1 month of treatment, with reductions ranging from 49-97% at 1 month and 45-98% by 3 months of therapy 1
- Surface IgE receptor density on effector cells decreases, meaning even if allergen is introduced during skin testing, there are fewer receptors available to trigger the allergic cascade 2, 3
Without adequate surface-bound IgE, mast cells and basophils cannot recognize allergens during skin prick or intradermal testing, preventing the wheal-and-flare response that indicates a positive test 2.
Clinical Implications
Allergy skin testing should be performed before initiating Xolair therapy, not during treatment. The drug's mechanism of action—blocking IgE from binding to effector cells—is precisely what makes skin testing unreliable 2, 3.
If allergy testing is needed in a patient already on Xolair:
- Consider serum-specific IgE testing (such as ImmunoCAP) instead of skin testing, though even total IgE levels increase 1.5-8.6 fold during treatment due to IgE-omalizumab complexes 1
- Discontinuation of Xolair would be required for skin testing to become reliable again, given the 26-day elimination half-life, though this may not be clinically appropriate for asthma control 2, 3
Important Caveat
The provided evidence focuses on omalizumab's mechanism and IgE suppression but does not explicitly address allergy testing protocols. However, the pharmacologic data makes clear that any test relying on IgE-mediated mast cell degranulation (skin prick, intradermal testing) will be suppressed during omalizumab therapy 1, 2, 3.