Total IgE: what it is, what it tells you and when it’s tested

IgE is the allergy antibody. Your body also makes it against parasites. A total IgE test measures how much you have in all, without telling you what you are allergic to.

When it’s tested

A doctor or allergist mostly orders it when they suspect an allergy, atopic eczema or allergic asthma. It is also used for some rare lung conditions, when a parasite is suspected, and before some treatments for severe asthma.

On its own it says little: to find out what you are allergic to, you need skin prick tests or specific IgE.

It is not a useful test for people who feel well and have no symptoms. That is why Rosa does not test it. Instead it looks at eosinophils, the white cells that rise with allergies and parasites, together with the rest of your blood count.

What it tells you, and what it does not

A high total IgE says your immune system tends to react in an allergic way, or that there is another cause to look for. It does not say what you are allergic to, or how serious an allergy is.

A normal total IgE does not rule out an allergy. Many allergic people, for example to a single pollen or food, have a normal total IgE.

Specific IgE, which many people still call RAST, is a different test: it measures antibodies against one thing, such as house dust mites, grass pollen or peanuts. Even then, being sensitised does not always mean having symptoms.

That is why it is read together with other tests:

Normal total IgE levels

There is no single value for everyone. Each lab sets its own limit, and in children it changes with age. For adults, almost all labs put the upper limit somewhere between about 80 and 150 kU/L.

So look at the limit printed on your report. A value just above it is common, even in people with no symptoms.

You do not need to fast. Antihistamines do not change this blood test: people having skin tests stop them, not people having a blood draw.

If your total IgE is high or low

Why total IgE is high

The most common causes come first.

What can muddy the picture

A few things make the result harder to read.

When to worry

Talk to your doctor if:

Frequently asked questions

What is a normal total IgE level? It depends on the lab and on age. In adults the upper limit is usually between about 80 and 150 kU/L. The limit printed on your own report is what counts.

What does a high total IgE mean? Often an allergy, atopic eczema or asthma. Sometimes smoking, less often a parasite or a rare condition. On its own it does not tell you what you are allergic to.

What is the difference between total IgE and specific IgE (RAST)? Total IgE is all the IgE in your blood. Specific IgE measures the IgE against one substance, such as dust mites or a food. To understand an allergy you usually need specific IgE or skin tests, read alongside your symptoms.

Can I be allergic with a normal total IgE? Yes. Many allergic people have a normal total IgE. If you have symptoms, an allergist picks the right tests.

Does Rosa test total IgE? No. Rosa measures eosinophils and the rest of your blood count, which can give a first sign of allergies or parasites. If your doctor wants IgE, they order it separately.

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