Blood tests to identify allergy.

What is an allergy blood test?

An allergy blood test is performed to identify a specific type of antibody (called immunoglobulin E — IgE) that the human immune system produces when it comes into contact with a substance that the person is allergic to (an allergen). Allergy blood tests are called serum allergen-specific IgE tests.

There are two main steps in developing an allergy. First, our immune system mistakenly identifies a substance that is normally harmless (an allergen) as harmful, and produces a specific IgE antibody to ‘combat’ it. This event is called by scientists ‘sensitisation’. Shortly after, when a person next encounters the allergen, the IgE recognises the allergen and an allergic reaction occurs. An allergic reaction may manifest itself as sneezing, coughing, skin rash or, in serious cases, anaphylactic shock – a potentially fatal condition. IgE attaches to cells called mast cells, triggering the release of a chemical called histamine. The medications that are commonly used for allergy are called antihistamines because they stop histamine from being produced.

Common allergens that affect people include pollens, house dust mite, moulds, some insects and animal dander (skin particles). Common food allergens include proteins in eggs, peanuts and tree nuts (such as walnuts), fish, shellfish, milk, wheat and soy. An allergy blood test can look for IgE reacting to one particular allergen or to a group of allergens.

Why is an allergy blood test done?

An allergy blood test may be done if you suspect that an allergic reaction could be causing your symptoms. The goal is to find out whether you are having an allergic reaction, and if so, to discover which allergen could be responsible for your symptoms. Once the allergen is identified, you can eliminate it from your environment or, if that is not possible, reduce the exposure.

How is an allergy blood test done?

For an allergy blood test, a blood sample will be taken from a vein. 

No special preparation is required for an allergy blood test.

Are there any risks of an allergy blood test?

Allergy blood tests are not considered to have any risks, other than slight discomfort when the blood is taken and occasionally bruising at the site of the blood test.

What happens after an allergy blood test?

Allergy blood tests can tell you whether you produce IgE in response to a specific allergen. If you have a negative test, it is very unlikely that you have an allergic reaction to that allergen.

A positive test indicates that you are sensitised to the allergen (that is, you produce specific IgE antibodies in response to it).