An allergy blood test measures a substance called immunoglobulin E (IgE) in your blood. IgE is an antibody that your body makes. If you have allergies, you may have more IgE in your blood than normal.

Allergies are a common, long-term condition that involves your immune system. Your immune system makes antibodies to fight off viruses, bacteria, and other things that can make you sick. With allergies, your immune system treats one or more harmless substances, such as pollen or peanuts, as a threat. To fight the "threat," your immune system makes IgE antibodies. This is what causes your allergy symptoms.

• A total IgE test is used to measure the total amount of IgE antibodies in your blood.
• A specific IgE test measures how much IgE your body makes in response to a single allergen. A separate test is done for each allergen that may be causing your allergies.