Immunoglobulin E (IgE)
IgE is the allergy antibody — triggers mast cells to release histamine causing allergic reactions. Least abundant immunoglobulin (<0.001% of total) but most potent for immediate reactions. Elevated IgE: allergic rhinitis, asthma, eczema, food allergies, parasitic infections (higher than allergies — IgE evolved to fight parasites!). Very high IgE (>1000): ABPA, hyper-IgE syndrome, severe eczema. Total IgE = overall allergic tendency. Specific IgE = identifies exact triggers. Required for omalizumab (anti-IgE) dosing in severe asthma.
Immunoglobulin E (IgE) is the antibody responsible for allergic reactions. Although it’s the least abundant antibody in blood — making up less than 0.001% of total immunoglobulins — IgE plays an outsized role in health, triggering the cascade of symptoms we recognize as allergies. When IgE binds to allergens like pollen, pet dander, or certain foods, it activates mast cells and basophils to release histamine and other inflammatory chemicals, causing sneezing, itching, hives, and in severe cases, anaphylaxis.
Why does this matter? Measuring total IgE provides insight into allergic status and helps evaluate patients with suspected allergic conditions, asthma, eczema, and chronic hives. Elevated IgE suggests an allergic tendency (atopy) and can point toward allergic causes of symptoms. IgE is also elevated in parasitic infections, reflecting its evolutionary role in fighting worms. Understanding your IgE level helps contextualize allergic symptoms and guide further allergy evaluation.
Beyond total IgE, specific IgE tests measure antibodies against individual allergens — identifying exactly what triggers your allergic reactions. Together, total and specific IgE testing forms the foundation of modern allergy diagnosis.
Key Benefits of Testing
Total IgE testing helps identify individuals with allergic tendency (atopy) and supports the diagnosis of allergic conditions. Elevated levels strengthen the case for allergic causes of symptoms like chronic rhinitis, asthma, or eczema. Very high IgE levels prompt evaluation for specific conditions including allergic bronchopulmonary aspergillosis (ABPA) and hyper-IgE syndrome.
For patients with asthma, IgE levels help determine eligibility for anti-IgE biologic therapy (omalizumab), which has transformed treatment of severe allergic asthma. IgE testing also screens for parasitic infections in appropriate clinical contexts.
What Does This Test Measure?
The total IgE test measures the overall concentration of immunoglobulin E antibodies in blood. This reflects your body’s combined IgE production against all allergens and other triggers, providing a general picture of IgE-mediated immune activity.
What IgE Does
IgE antibodies evolved primarily to fight parasitic worms (helminths). When bound to parasites, IgE triggers eosinophils and other cells to release toxic substances that damage the invaders. In modern environments with fewer parasitic infections, this same IgE system often misfires against harmless substances — pollen, dust mites, foods — causing allergies.
The allergic reaction process works like this: First, your immune system encounters an allergen and produces specific IgE antibodies against it (sensitization). These IgE antibodies attach to mast cells in tissues and basophils in blood, essentially “arming” them. On subsequent exposure, the allergen binds to its specific IgE on mast cell surfaces, cross-linking the antibodies. This cross-linking triggers mast cell degranulation — the explosive release of histamine, leukotrienes, and other inflammatory mediators that cause allergic symptoms within minutes.
Total IgE vs Specific IgE
Total IgE measures all IgE antibodies combined, regardless of what they target. It indicates overall allergic tendency but doesn’t identify specific triggers. Normal total IgE doesn’t exclude allergies, and elevated total IgE doesn’t prove specific allergies.
Specific IgE tests measure antibodies against individual allergens — cat dander, peanut, dust mite, specific pollens. These tests identify exactly what you’re sensitized to and are more useful for diagnosing and managing specific allergies. Specific IgE testing has largely replaced skin prick testing in many clinical settings.
IgE Compared to Other Immunoglobulins
The body produces five classes of antibodies, each with different functions. IgG is the most abundant, providing long-term immunity. IgA protects mucosal surfaces. IgM is the first responder to new infections. IgD’s function is less understood. IgE, though present in trace amounts, is the most potent trigger of immediate inflammatory responses — which is why tiny amounts can cause dramatic allergic reactions.
Why This Test Matters
Evaluates Allergic Conditions
Total IgE helps assess patients with suspected allergic disease. Elevated levels support (but don’t prove) allergic etiology for conditions like allergic rhinitis, allergic asthma, atopic dermatitis, food allergies, and chronic urticaria. The higher the IgE, the stronger the suggestion of allergic involvement, though significant overlap exists between allergic and non-allergic individuals.
Guides Asthma Management
In asthma, IgE levels help characterize disease phenotype. Allergic (atopic) asthma features elevated IgE and responds well to treatments targeting allergic inflammation. Total IgE level is specifically required to determine dosing for omalizumab (Xolair), an anti-IgE monoclonal antibody that has revolutionized treatment of moderate-to-severe allergic asthma.
Detects Parasitic Infections
IgE evolved to fight parasites, and parasitic worm infections typically cause marked IgE elevation — often much higher than allergic conditions. In patients with elevated IgE and appropriate risk factors (travel to endemic areas, immigration), parasitic infection should be considered alongside allergic conditions.
Identifies Specific Syndromes
Extremely elevated IgE levels (often >1000-2000 IU/mL) occur in specific conditions requiring recognition:
- Allergic bronchopulmonary aspergillosis (ABPA): Fungal hypersensitivity in the lungs, often in asthmatics
- Hyper-IgE syndrome (Job syndrome): Primary immunodeficiency with very high IgE, recurrent infections, and eczema
- Severe atopic dermatitis: Can cause markedly elevated IgE
- Churg-Strauss syndrome (EGPA): Eosinophilic vasculitis with high IgE
Value of Baseline Testing
Knowing your baseline IgE level provides useful context for future health decisions. If you later develop respiratory symptoms or skin problems, having a prior IgE result helps determine whether allergic evaluation is warranted. Establishing baseline also helps interpret changes over time.
What Can Affect IgE Levels?
Causes of Elevated IgE
Allergic conditions are the most common cause in developed countries:
- Allergic rhinitis (hay fever)
- Allergic asthma
- Atopic dermatitis (eczema)
- Food allergies
- Allergic conjunctivitis
- Chronic urticaria (some cases)
Parasitic infections typically cause higher IgE elevations than allergies:
- Ascaris (roundworm)
- Hookworm
- Strongyloides
- Toxocara
- Schistosomiasis
- Many other helminths
Immunologic conditions:
- Hyper-IgE syndrome (Job syndrome)
- Allergic bronchopulmonary aspergillosis (ABPA)
- Wiskott-Aldrich syndrome
- Omenn syndrome
- Some other primary immunodeficiencies
Other causes:
- Churg-Strauss syndrome (EGPA)
- Certain malignancies (Hodgkin lymphoma, IgE myeloma — rare)
- Some infections (HIV, EBV — variable)
- Drug reactions
Causes of Low IgE
Low IgE is less commonly clinically significant but occurs with certain primary immunodeficiencies, inherited IgE deficiency (rare, usually asymptomatic), and some acquired immunodeficiency states.
Normal Variations
IgE levels vary with age — low at birth, rising through childhood, peaking in adolescence, then gradually declining. Males tend to have slightly higher levels than females. Significant individual variation exists; some non-allergic individuals have higher IgE than some allergic individuals.
When Should You Get Tested?
Suspected allergic conditions: Chronic nasal congestion, sneezing, and itchy eyes suggesting allergic rhinitis. Recurrent wheezing or coughing suggesting allergic asthma. Chronic itchy skin rashes suggesting atopic dermatitis. Symptoms after eating certain foods suggesting food allergy.
Asthma evaluation: Determining whether asthma is allergic (atopic) helps guide treatment selection. IgE testing is required before prescribing omalizumab for severe allergic asthma.
Suspected parasitic infection: Travel to endemic areas with subsequent eosinophilia or unexplained symptoms. IgE elevation supports parasitic etiology.
Evaluation of specific conditions: Suspected ABPA in asthmatics with recurrent pulmonary infiltrates. Suspected hyper-IgE syndrome with recurrent infections and eczema.
Chronic urticaria evaluation: Although most chronic hives are not IgE-mediated, testing helps characterize the condition.
Understanding Your Results
Total IgE results are reported in International Units per milliliter (IU/mL) or kilounits per liter (kU/L), which are equivalent.
Normal IgE generally argues against significant allergic disease as the cause of symptoms, though specific allergies can exist with normal total IgE. Normal levels are reassuring but don’t completely exclude allergic conditions.
Mildly elevated IgE is consistent with allergic conditions and supports allergic etiology of symptoms. However, it’s nonspecific — many people have mildly elevated IgE without significant allergic disease.
Moderately elevated IgE increases likelihood of allergic conditions. Consider specific IgE testing to identify triggers. In asthmatics, this range typically qualifies for anti-IgE therapy if criteria are met.
Markedly elevated IgE (>1000 IU/mL) suggests either severe allergic disease, parasitic infection, or specific syndromes like ABPA or hyper-IgE syndrome. Further evaluation is warranted to determine the cause.
Important Limitations
Total IgE has significant limitations as an allergy test. Many allergic individuals have normal total IgE. Elevated IgE doesn’t identify which allergens are triggers. The test cannot diagnose or exclude specific allergies — specific IgE testing or skin prick testing is needed for that. Total IgE is best used as one piece of information alongside clinical history and other testing.
What to Do About Abnormal Results
For Elevated IgE
Correlate with symptoms. Elevated IgE in someone with allergic symptoms supports allergic diagnosis. Elevated IgE without allergic symptoms may warrant monitoring but not necessarily treatment.
Consider specific IgE testing to identify which allergens you’re sensitized to. Panels can test for common environmental allergens (dust mites, molds, pollens, pet dander) or food allergens based on clinical suspicion.
Evaluate for parasites if IgE is very high or if there’s travel history, immigration from endemic areas, or eosinophilia. Stool studies and serologic testing may be indicated.
Consider specific conditions if IgE is extremely elevated (>1000-2000 IU/mL). In asthmatics, evaluate for ABPA with Aspergillus-specific IgE and imaging. Consider hyper-IgE syndrome if there’s history of recurrent infections and eczema.
Allergy consultation may be helpful for comprehensive evaluation and management planning, especially for moderate-to-severe allergic conditions.
For Normal IgE with Allergic Symptoms
Normal total IgE doesn’t exclude allergies. Proceed with specific IgE testing or skin prick testing to identify specific sensitivities. Some allergic individuals have normal total IgE but positive specific IgE to their triggers.
Related Health Conditions
Allergic Rhinitis
Allergic rhinitis (hay fever) affects up to 30% of adults and commonly elevates total IgE. Symptoms include sneezing, nasal congestion, runny nose, and itchy eyes triggered by pollens, dust mites, mold, or pet dander. Specific IgE testing identifies triggers for avoidance strategies and immunotherapy consideration. Learn more →
Allergic Asthma
Allergic asthma is triggered by inhaled allergens and characterized by elevated IgE and positive specific IgE tests. It’s the most common asthma phenotype in children and common in adults. IgE level determines eligibility for omalizumab (anti-IgE therapy), which reduces asthma exacerbations and improves control in severe cases. Learn more →
Atopic Dermatitis
Atopic dermatitis (eczema) frequently features elevated IgE, often markedly so in severe cases. The condition involves skin barrier dysfunction and immune dysregulation with a strong allergic component. IgE elevation correlates with disease severity in many patients. Newer biologics targeting the IgE pathway are emerging treatments. Learn more →
Food Allergies
IgE-mediated food allergies cause reactions ranging from hives to anaphylaxis. Common triggers include peanuts, tree nuts, shellfish, fish, milk, eggs, wheat, and soy. Specific IgE testing to suspected foods helps confirm diagnosis, though correlation with clinical reactivity isn’t perfect. Learn more →
Parasitic Infections
Parasitic worm infections typically cause higher IgE elevations than allergic conditions — IgE evolved to fight parasites. Markedly elevated IgE with eosinophilia in someone with travel history or appropriate risk factors strongly suggests parasitic infection requiring specific evaluation and treatment. Learn more →
Allergic Bronchopulmonary Aspergillosis (ABPA)
ABPA is a hypersensitivity reaction to Aspergillus fungus in the airways, usually occurring in asthmatics or cystic fibrosis patients. It causes very high total IgE (typically >1000 IU/mL), elevated Aspergillus-specific IgE, pulmonary infiltrates, and bronchiectasis. Recognition and treatment prevents progressive lung damage. Learn more →
Hyper-IgE Syndrome
Hyper-IgE syndrome (Job syndrome) is a rare primary immunodeficiency characterized by extremely high IgE (often >2000 IU/mL), recurrent staphylococcal skin and lung infections, severe eczema, and distinctive facial features. It’s caused by STAT3 mutations in most cases and requires specialized immunologic management. Learn more →
Related Biomarkers Often Tested Together
Specific IgE Testing — Identifies exactly which allergens you’re sensitized to.
Eosinophils — Often elevated alongside IgE in allergic conditions and parasitic infections.
Tryptase — Mast cell marker; elevated after anaphylaxis or in mastocytosis.
Complete Blood Count — Includes eosinophil count; helps evaluate allergic and parasitic conditions.
Total IgA — Another immunoglobulin; low IgA can affect interpretation of some allergy tests.
Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.
Frequently Asked Questions
Immunoglobulin E (IgE) is the antibody responsible for allergic reactions. When IgE binds to allergens, it triggers mast cells to release histamine and other chemicals causing allergy symptoms. IgE evolved to fight parasites but in modern environments often reacts to harmless substances like pollen and food proteins.
Elevated IgE suggests allergic tendency or parasitic infection. Common causes include allergic rhinitis, asthma, eczema, food allergies, and parasitic worm infections. Very high levels may indicate specific conditions like ABPA or hyper-IgE syndrome.
Yes — total IgE can be normal even in allergic individuals. The test measures all IgE combined; you might have significant specific IgE to your triggers while total IgE remains normal. Specific IgE testing is more useful for identifying individual allergens.
Total IgE measures all IgE antibodies combined. Specific IgE tests measure antibodies against individual allergens (cat, peanut, dust mite, etc.). Total IgE indicates allergic tendency; specific IgE identifies your actual triggers.
IgE helps determine if asthma is allergic (atopic), which affects treatment choices. It’s also required for prescribing omalizumab (Xolair), an anti-IgE biologic that helps control severe allergic asthma by blocking IgE from triggering reactions.
Yes — parasitic worm infections typically cause marked IgE elevation, often higher than allergic conditions. This reflects IgE’s evolutionary role in fighting parasites. High IgE with eosinophilia and relevant exposure history suggests parasitic infection.
No fasting is required for IgE testing. You can eat and drink normally before your blood draw.
References
Key Sources:
- Platts-Mills TAE. The allergy epidemics: 1870-2010. J Allergy Clin Immunol. 2015;136(1):62-68.
- Gould HJ, Sutton BJ. IgE in allergy and asthma today. Nat Rev Immunol. 2008;8(3):205-217.
- Bousquet J, et al. Allergic Rhinitis and its Impact on Asthma (ARIA) 2008 Update. Allergy. 2008;63(Suppl 86):8-160.
