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IgG and IgE Testing: What Each Antibody Actually Shows
IgE identifies true allergy. IgG mostly reflects what you eat. What each test shows, what the allergy bodies say about IgG panels, and how to investigate food symptoms properly.
IgG and IgE sound like variations on the same test. They are not. One is the validated way to diagnose allergy; the other reflects which foods you have been eating. Both are sold as “food allergy testing”, and the confusion between them leads a great many people to remove foods they never needed to. This guide explains what each antibody genuinely shows.
Key takeaways
- IgE is the antibody involved in true allergy. Testing for it is validated and diagnostic when read with your history.
- IgG indicates exposure to a food, not an adverse reaction to it. High IgG usually reflects what you eat most.
- Major allergy organisations do not recommend IgG testing for diagnosing food allergy or intolerance.
- If IgG is used at all, its value comes from the structured elimination that follows, not from the result itself.
Two antibodies, two different questions
| IgE | IgG | |
|---|---|---|
| What it indicates | An allergic immune response | Exposure to a food |
| Reaction speed | Minutes to two hours | Not linked to any timed reaction |
| Can it be life-threatening? | Yes — IgE mediates anaphylaxis | No |
| Clinically validated? | Yes, for allergy diagnosis | Not for diagnosing allergy or intolerance |
| Typical result pattern | Positive to a small number of specific foods | Positive to many foods, often the ones eaten daily |
| Endorsed by allergy bodies? | Yes | No |
IgE: the allergy antibody
In a true food allergy, the immune system produces IgE antibodies against a specific food protein. On re-exposure those antibodies trigger histamine release, producing hives, swelling, vomiting, wheeze or, at the severe end, anaphylaxis.
Specific IgE blood testing measures antibodies to individual allergens and is used alongside skin prick testing. Both share one limitation worth understanding: a positive result shows sensitisation, not necessarily clinical allergy. People commonly test positive to foods they eat regularly with no trouble at all.
This is why the clinical history does the real diagnostic work. A positive IgE to prawn in someone who develops hives within twenty minutes of eating prawn is meaningful. The same result in someone who eats prawn weekly without incident usually is not.
IgG: what it actually reflects
IgG is the most abundant antibody class in your blood and forms part of normal immune memory. When you eat a food, your immune system encounters its proteins and may produce IgG to it. That is a normal response to exposure, not evidence of harm.
Which is why IgG panels tend to produce results that look dramatic and read predictably. Someone eating rice daily will usually show IgG to rice. Wheat, dairy, egg and soy appear frequently on positive lists precisely because they are the foods most people eat most often. There is research suggesting IgG4 in particular may reflect tolerance to a food rather than intolerance — close to the opposite of how the results are often presented.
What the professional bodies say. The major international allergy and immunology organisations advise against IgG testing for the diagnosis of food allergy or food intolerance, on the grounds that IgG indicates exposure rather than an adverse reaction. This is worth knowing before paying for a panel, and worth weighing against any clinic that presents IgG results as a definitive list of foods to avoid.
Where a structured approach does help
None of this means the symptoms are imaginary. Bloating, fatigue, headaches and digestive discomfort after eating are real, common, and worth investigating properly. The difficulty is that no blood test currently identifies food intolerance reliably.
What does work is structured elimination and reintroduction — unglamorous, slower, and considerably more informative:
- Record first. Two to three weeks of dated food and symptom notes. This alone often narrows the field, and sometimes identifies the trigger outright.
- Remove one suspect at a time. Cutting several foods simultaneously tells you nothing about which one mattered.
- Allow two to four weeks. Long enough for a genuine change to appear, short enough to avoid unnecessary restriction.
- Reintroduce deliberately. This is the step that produces the answer, and the one most often skipped. If symptoms do not return, that food was never the problem.
- Protect nutrition throughout. Removing dairy, wheat or whole food groups without replacement has consequences worth planning around.
If an IgG panel has already been done, the sensible use of it is as a rough shortlist to test through this process — not as a list of foods to avoid indefinitely. The value sits in the reintroduction, which is what turns a suspicion into an answer.
What else is worth ruling out
Several conditions produce exactly the symptoms IgG panels are usually bought to explain, and each has a proper test:
- Coeliac disease — tested with tTG-IgA antibodies, and only valid while you are still eating gluten.
- Lactose intolerance — confirmed with a hydrogen breath test, or a structured dairy trial.
- Small intestinal bacterial overgrowth — also assessed by breath testing.
- Irritable bowel syndrome — which frequently responds to a supervised low-FODMAP approach rather than open-ended avoidance.
- Iron, B12 or vitamin D deficiency — common causes of fatigue often blamed on food sensitivity.
The distinction between allergy and intolerance is where most of the confusion starts — we cover it in food allergy vs food intolerance , and the specific considerations for children in allergy in children .
At HDC Medical, this work is dietitian-led. IgE testing is used where allergy is genuinely suspected, and any elimination comes with a structured reintroduction plan and nutritional cover rather than a list of foods to avoid indefinitely. Related markers can be included within a full health screening .
Reviewed by Jess Yii Poh Kee
Clinical Dietitian · Functional Nutritionist · BHSc Nutritional & Dietetic Medicine
Jess leads HDC Medical's allergy and functional nutrition work, with Australian clinical training in nutritional and functional medicine. View the full profile →
This article is for general education and does not replace personalised medical advice. Reference ranges vary between laboratories — always interpret your results with a qualified professional. Blood screening is a monitoring and early-flag tool, not a diagnosis. HDC Medical is a dietitian-led health screening centre in Oval Damansara, Kuala Lumpur.
Frequently asked questions
What is the difference between IgG and IgE testing?
IgE identifies true allergy and is clinically validated for that purpose. IgG reflects exposure to a food rather than a reaction to it, and is not recommended for diagnosing food allergy or intolerance.
Why did my IgG test flag so many foods?
Because IgG tracks what you eat. The foods appearing most often on positive lists are usually the ones in your diet most often, which is a normal immune response rather than evidence of a problem.
Is there a reliable blood test for food intolerance?
No. Structured elimination and reintroduction remains the most dependable method, with hydrogen breath testing available specifically for lactose and fructose malabsorption.
I already paid for an IgG test. Was it wasted?
Not entirely, if it is used sensibly. Treat the results as a shortlist to test through proper elimination and reintroduction rather than a list of foods to avoid permanently. The reintroduction step is what produces the answer.
Which test should I ask for if I react to food?
It depends on the reaction. Rapid symptoms involving skin, swelling or breathing point to allergy, where IgE testing is appropriate. Slower digestive symptoms point to intolerance, which is investigated through structured elimination rather than a blood test.
Find out which food is the problem — properly.
Book a dietitian-led assessment at HDC Medical in Kuala Lumpur — the right test for your symptoms, and a structured plan that includes reintroduction.
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