Overview
Immunoglobulin E (IgE) is a type of antibody produced by the immune system. Antibodies are special proteins that help the body detect and fight harmful substances. IgE, in particular, is mainly involved in allergic reactions and in defending the body against parasitic infections.
When a person has an allergy, their immune system becomes overly sensitive to harmless substances such as pollen, dust, food, or animal dander. As a reaction, the body produces high levels of IgE, which then trigger symptoms like sneezing, itching, rashes, or breathing problems.
The IgE blood test measures the amount of this antibody in the blood. It is commonly used to diagnose allergies, asthma, and sometimes to check for parasitic infections or immune disorders.
What Is IgE? – A Simple Explanation
IgE belongs to the immunoglobulin family, which includes IgA, IgG, IgM, IgD, and IgE. Among these, IgE is the least abundant in the blood, but it has a powerful effect because it triggers strong allergic and inflammatory responses.
Even small increases in IgE can cause significant symptoms, which is why the IgE test is an important tool for allergy diagnosis.
Where Is IgE Produced in the Body?
IgE is made by plasma cells, which are specialized white blood cells that originate from B lymphocytes. These plasma cells are present in:
- Lymph nodes
- Spleen
- Bone marrow
- Mucosal surfaces (nose, lungs, intestines)
- Skin-associated lymphoid tissues
When the body comes in contact with an allergen, these plasma cells produce IgE antibodies. These antibodies attach to mast cells and basophils, which are responsible for releasing histamine and causing allergy symptoms.
Main Functions and Importance of IgE
1. Triggers Allergic Reactions
IgE binds to allergens such as pollen, dust mites, food proteins, insect venom, or animal dander. Once attached, it activates mast cells and basophils, causing them to release histamine and other chemicals that result in:
- Sneezing
- Red eyes
- Skin itching
- Hives
- Swelling
- Breathing problems
2. Defense Against Parasitic Infections
IgE plays a protective role against certain parasites, including:
- Helminths
- Hookworms
- Schistosoma
- Strongyloides
These infections can increase IgE levels significantly.
3. Helps Diagnose Allergies and Immune Disorders
Doctors use IgE levels to:
- Diagnose allergic diseases
- Monitor asthma severity
- Detect parasitic infections
- Screen for rare immune conditions like Hyper-IgE Syndrome
- Evaluate chronic skin disorders like eczema
Causes of Low or Negative IgE Levels
Low IgE levels are considered normal for most healthy people because IgE is naturally present in small amounts.
Common Causes
- Normal immune function
- Genetic IgE deficiency (rare)
- Certain primary immunodeficiency disorders
Is low IgE dangerous?
Usually, no. Most people with low IgE have no symptoms at all. Only in rare cases of immune deficiency do people experience more frequent:
- Sinus infections
- Ear infections
- Lung infections
Symptoms of Low IgE Levels
Most individuals do not have any symptoms.
In rare cases involving immune disorders, symptoms may include:
- Recurrent bacterial infections
- Recurrent viral infections
- Chronic sinusitis or pneumonia
These symptoms require further immune testing.
Causes of High or Positive IgE Levels
High IgE levels are more common and usually indicate an overactive immune response.
1. Allergic Conditions
- Hay fever (allergic rhinitis)
- Asthma
- Atopic dermatitis (eczema)
- Food allergies
- Drug allergies
- Animal dander allergy
- Insect venom allergy
2. Parasitic Infections
IgE rises sharply with parasites, especially:
- Strongyloides
- Hookworm
- Schistosomiasis
- Ascaris
3. Immune Disorders
- Hyper-IgE syndrome (Job syndrome)
- Some primary immunodeficiency diseases
4. Certain Cancers
- Hodgkin’s lymphoma
- IgE myeloma (rare cancer of plasma cells)
Symptoms of High IgE Levels
Symptoms depend on the underlying cause.
Allergy Symptoms
- Sneezing
- Runny or blocked nose
- Itchy or watery eyes
- Skin rashes
- Hives (urticaria)
- Swelling
- Coughing or wheezing
Asthma Symptoms
- Shortness of breath
- Chest tightness
- Wheezing
- Dry cough
Parasitic Infection Symptoms
- Abdominal pain
- Diarrhea
- Weight loss
- Anemia
- Weakness
Severe Allergic Reaction (Anaphylaxis)
This is a medical emergency:
- Sudden swelling
- Difficulty breathing
- Low blood pressure
- Rapid pulse
- Loss of consciousness
Reference Ranges for IgE
Normal IgE levels vary depending on age and lab method.
Adults
- Normal: <100–150 IU/mL
- Mild elevation: 150–500 IU/mL
- Moderate elevation: 500–1000 IU/mL
- Very high: >1000 IU/mL (suggests strong allergic reaction or parasitic infection)
Children
Children naturally have higher IgE due to developing immunity.
Sample Type and Testing Method
The test requires a blood sample taken from a vein in the arm.
Types of IgE Tests
1. Total IgE Test
Measures overall IgE level in the body.
2. Specific IgE Test (Allergen-specific tests)
Detects IgE antibodies against individual allergens using methods like:
- RAST
- ImmunoCAP
- ELISA
These help identify specific triggers such as peanuts, dust mites, milk, pollen, or latex.
Test Preparation
- No fasting required
- No medication restrictions unless your doctor advises otherwise
- Inform your doctor if you are taking antihistamines or steroids (these do not affect IgE blood results but may affect skin allergy tests)
- For accurate allergy diagnosis, share your symptom history
When to Consult a Doctor
See a doctor or allergist if:
- You have frequent sneezing or runny nose
- You suspect food allergy
- You have chronic skin itching or eczema
- You have asthma symptoms
- You experience hives or unexplained rashes
- You have signs of parasitic infection
- You had a severe allergic reaction (anaphylaxis)
- Your child shows recurrent breathing problems or allergies
Important Word Explanations
- Antibody: A protein that fights infections and foreign substances.
- Allergen: A substance that causes an allergic reaction.
- Histamine: A chemical responsible for allergy symptoms.
- Mast Cells: Immune cells that release histamine.
- ImmunoCAP: A test that measures specific IgE levels.
- Anaphylaxis: A severe, life-threatening allergic reaction.
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