IgE vs IgG: The Ultimate Guide to Allergy, Intolerance, and Antibody Blood Tests

Navigating the world of allergy testing can be confusing, especially with terms like IgE, IgG, antibody, and immunoglobulin being used frequently. You might wonder what the difference is between an allergy and an intolerance, or which blood test is right for you.

This article demystifies the complex relationship between different types of antibodies, particularly IgE and IgG, and their roles in diagnosing food allergies and food sensitivities.

We will explore what each test measures, what the results mean, and why understanding the IgE vs IgG distinction is crucial for accurate allergy diagnosis and management. Read on to discover the key differences and gain clarity on how to approach testing for food-related issues.

What Are Immunoglobulins and Why Are These Antibodies Important?

Immunoglobulins, or antibodies, are key players in your immune system.

Antibodies are proteins in your body that help fight off things like germs and viruses. They’re shaped like a “Y,” with the tips specially made to grab onto a specific invader. Once they stick to the invader, they either stop it from causing harm or call other parts of your immune system to get rid of it. This helps protect you from getting sick and helps your body remember how to fight off infections in the future.

There are different types of antibodies that do different jobs. Some act fast when you first get sick, others protect areas like your lungs and stomach, and some help your immune cells get started.

When it comes to allergies or food reactions, two types called IgE and IgG are important. IgE causes true allergic reactions like itching or swelling, while IgG is linked to other kinds of food issues. Knowing the difference helps figure out what’s really going on with your body.

What is an IgE Antibody and How Does It Relate to a True Allergy?

Immunoglobulin E, or IgE, is the antibody mainly responsible for true allergic reactions.

Although it’s the least common antibody in your blood, it has a big impact. In people with allergies, the immune system wrongly sees harmless things like peanut protein, pollen, or pet dander as threats. This causes the body to make IgE antibodies that specifically target those allergens.

During the first exposure, these IgE antibodies attach to immune cells called mast cells and basophils, which are found in the skin, lungs, and digestive system.

The next time you’re exposed to the same allergen, it sticks to the IgE on these cells, triggering them to release chemicals like histamine. These chemicals cause typical allergy symptoms (like swelling, redness, sneezing, or tightening of airways), and in serious cases, can lead to a life-threatening reaction called anaphylaxis.

This process explains why allergic reactions happen so quickly and why they can range from mild to severe.

How Does a Standard IgE Allergy Test Work?

An IgE allergy test is the trusted way to help diagnose a true allergy by measuring the amount of allergen-specific IgE antibodies in your blood. During the test, a blood sample is taken and sent to a lab, where it’s exposed to different suspected allergens. The test then measures how much IgE binds to each one, with results shown in units per liter. Finding specific IgE means you’re sensitized to that allergen, which is a necessary step for having an allergic reaction.

However, having IgE antibodies doesn’t always mean you’ll have symptoms. Some people tolerate the allergen just fine. This test is especially useful for those who can’t have skin tests, like people with skin conditions, infants, or those who can’t stop taking antihistamines.

Doctors use the IgE test results along with your symptoms and history to make a clear diagnosis. 

What is an IgG Antibody and What is its Role in the Body?

Immunoglobulin G, or IgG, is the most common antibody in your blood and tissues. It plays a major role in protecting you long-term against infections. After you’ve had an infection or vaccine, your body makes IgG antibodies that remember the invader. If the same germ shows up again, these antibodies quickly recognize and fight it off, helping keep you healthy.

IgG is also special because it can cross the placenta, giving babies protection before they’re born.

It’s normal for your body to make IgG antibodies against foods you eat. When food proteins enter your bloodstream, your immune system recognizes them but usually doesn’t see them as harmful. In fact, one type of IgG, called IgG4, actually helps your body build tolerance to allergens. For example, during allergy treatments, IgG4 levels rise as your immune system learns to tolerate certain substances, reducing allergic reactions. So, having IgG antibodies to food is usually a sign of normal immune function, not a problem.

Why is IgG and IGE Testing for Food Allergies so Controversial?

The confusion around IgG and IgE testings comes from people misunderstanding how it works and using it incorrectly to diagnose food problems. 

IgE testing is the trusted, science-backed way to find true allergies. It’s better understood how IgE antibodies cause quick allergic reactions, like hives or trouble breathing, and doctors use IgE tests to help diagnose these allergies.

On the other hand, using IgG tests to find “food sensitivities” or delayed food allergies isn’t well-supported by science and is actually discouraged by leading allergy experts. IgG antibodies to foods are normal and just show that you’ve eaten those foods. So, if an IgG test shows high levels for common foods like wheat or dairy, it usually just means you eat them regularly, not that you’re allergic. Relying on these tests can lead to unnecessary diets that cut out important foods, which might cause nutrition problems and stress without fixing any real issues.

The key difference is how the two antibodies work. IgE causes immediate allergic reactions that can be serious, and IgE tests help confirm this. IgG, however, is more about your body recognizing foods you’ve eaten, often helping build tolerance, not causing harm. So, high IgG levels usually mean your immune system is doing its job, not that you have a food allergy or sensitivity.

Can an IgG Test Reliably Diagnose Food Sensitivities or Intolerance?

Based on current scientific evidence, IgG tests cannot reliably diagnose food sensitivities or intolerances. Since having food-specific IgG in your blood is a normal response to eating those foods, a positive/high IgG results often just reflect what you regularly eat, which can cause confusion and unnecessary diet restrictions.

It’s important to understand the difference between food intolerance and food sensitivity. Food intolerance is not an immune reaction but usually happens because your body lacks certain enzymes, like in lactose intolerance. Symptoms are often digestive and depend on how much of the food you eat.

IgG tests don’t measure these enzyme issues, so they can’t diagnose intolerances. Food sensitivity is a vague term for reactions that aren’t classic allergies. While some immune responses exist beyond IgE allergies, IgG testing isn’t proven to detect them. The best way to find non-allergic food problems is through a doctor-supervised elimination diet and carefully reintroducing foods to see what causes symptoms.

Making Sense of Your Results: What to Do After an IgG and IgE Test?

Interpreting test results the right way is key to managing your health effectively, and what you do depends a lot on which test you took.

If you had an IgE test and it’s positive, it means you’re sensitized to that allergen. But this only confirms an allergy if your symptoms match the test (like getting hives after eating shrimp). Your doctor will then help you create a plan to avoid the allergen, learn how to read labels, prevent cross-contamination, and be ready for emergencies. For serious allergies, you’ll likely get an epinephrine auto-injector and training on how to use it.

If you had an IgG test, be cautious with the results. High IgG levels just show exposure to foods, not a food allergy or sensitivity. Experts agree you shouldn’t change your diet based on IgG tests alone. Instead, talk with a healthcare professional or dietitian about your symptoms. They can help you find the real cause, often using trusted methods like elimination diets and food challenges, which are safer and more reliable than relying on IgG testing. This approach helps avoid unnecessary diet restrictions and keeps you healthy both physically and mentally.

Summary

• IgE vs. IgG: IgE antibodies drive immediate, true allergic reactions, which can be life-threatening. IgG antibodies are part of the body’s normal immune memory; their presence against food indicates exposure and often tolerance, not an allergy.
• Allergy Testing: An IgE test (blood or skin prick) is the scientifically validated method used to help diagnose a true allergy. It must be interpreted alongside a patient’s clinical history.
• IgG Test Controversy: IgG testing for food sensitivities is not scientifically supported or recommended by medical organizations. Results typically reflect your diet and can lead to harmful, unnecessary food restrictions.
• Intolerance vs. Allergy: A food intolerance (e.g., lactose intolerance) is a metabolic issue, not an immune reaction. Neither IgE nor IgG tests can diagnose an intolerance.
• Consult a Healthcare Professional: Always work with a qualified allergist or healthcare provider to diagnose food-related issues. They can provide an accurate diagnosis and create a safe, evidence-based management plan, steering you away from unreliable tests and toward genuine health solutions.

Further References

1. The myth of IgG food panel testing | AAAAI [Internet]. Aaaai.org. 2012. Available from: https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/igg-food-test

2. Carr S, Chan E, Lavine E, Moote W. CSACI Position statement on the testing of food-specific IgG. Allergy, Asthma & Clinical Immunology [Internet]. 2012 Jul 26;8(1). Available from: https://aacijournal.biomedcentral.com/articles/10.1186/1710-1492-8-12
3. Sicherer SH, Sampson HA. Food allergy: A review and Update on epidemiology, pathogenesis, diagnosis, prevention, and Management. The Journal of Allergy and Clinical Immunology [Internet]. 2018 Jan;141(1):41–58. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29157945
4. Gargano D, Appanna R, Santonicola A, De Bartolomeis F, Stellato C, Cianferoni A, et al. Food Allergy and Intolerance: A Narrative Review on Nutritional Concerns. Nutrients. 2021 May 13;13(5):1638.
5. All About Allergy Testing | AAAAI [Internet]. Aaaai.org. 2022. Available from: https://www.aaaai.org/Tools-for-the-Public/Conditions-Library/Allergies/all-about-allergy-testing
6. Stapel SO, Asero R, Ballmer-Weber BK, Knol EF, Strobel S, Vieths S, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Allergy [Internet]. 2008;63(7):793–6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/18489614
7. BDA. Food Allergy Testing Food Fact Sheet [Internet]. www.bda.uk.com. 2021. Available from: https://www.bda.uk.com/resource/food-allergy-intolerance-testing.html

Disclaimer: This article is for educational purposes only. Please consult your healthcare provider for personalized medical advice.