Allergy Blood Test

An allergy blood test measures the amount of allergy-causing antibodies called immunoglobulin E (IgE). Antibodies are proteins that your immune system makes to fight foreign substances, such as viruses and bacteria. But your immune system may also make them in response to allergens.

These are harmless substances, such as pollen and peanuts, that may cause an allergic reaction in some people. It's normal to have small amounts of IgE in your blood. But when you have an allergic reaction, your immune system sees the allergens as a threat and makes IgE antibodies.

This increases the amount of IgE in your blood and causes your allergy symptoms. Common allergens include: Pollen; Dust; Mold; Animal dander; Certain foods, including nuts and shellfish; Certain medicines, such as penicillin; Allergy symptoms can be mild to severe, depending on the type of allergy you have. They can range from itching and sneezing to asthma or even a life-threatening condition called anaphylactic shock.

Why this test is done

Your health care provider may order allergy testing if you have symptoms of an allergy. These include:

• Stuffy or runny nose
• Sneezing
• Itchy, watery eyes
• Hives (itchy raised red patches on your skin)
• Diarrhea
• Vomiting
• Shortness of breath
• Coughing
• Wheezing

Your provider may order an allergy blood test if you can't have allergy skin testing. Skin testing involves putting allergens directly on or into your skin. You may not be able to have skin testing if you:

• Have certain skin conditions
• Take certain medicines that may affect the results of the test
• Are likely to have a serious allergic reaction to the allergens used in skin testing

In certain cases, providers may order allergy blood tests for young children because skin testing may be too uncomfortable for them.

How to prepare

You don't need any special preparations for an allergy blood test. You may need to stop taking certain medicines before this test, such as antihistamines, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

Sample type

Blood

Other names for this test

IgE allergy test, Quantitative IgE, Immunoglobulin E, Total IgE, Specific IgE, RAST, CAP, ELISA, Allergy Screen