Skip navigation

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

URL of this page: https://medlineplus.gov/lab-tests/allergy-blood-test/

Allergy Blood Test

What is an Allergy Blood Test?

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.

Harmless substances that may cause allergies are called allergens. Common allergens include:

  • Pollen
  • Dust
  • Mold
  • Animal dander
  • Certain foods, including nuts and shellfish
  • Certain medicines, such as penicillin.

Allergy symptoms depend on the type of allergy you have. They can range from itching and sneezing to asthma or a life-threatening condition called anaphylactic shock.

Other names: IgE allergy test, Quantitative IgE, Immunoglobulin E, Total IgE, Specific IgE, RAST, CAP, ELISA

What is it used for?

Allergy blood tests are used to help find out if you have an allergy. There are two general types of allergy blood tests:

  • 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.

Why do I need an allergy blood test?

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

Your provider may choose to 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.

What happens during an allergy blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for an allergy blood test.

Are there any risks to the test?

There is very little risk to having an allergy blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

A total IgE test result that is high means that you may have some kind of allergy. But the results of a total IgE test don't show what you're allergic to or how serious your allergy may be.

A specific IgE test result that is high means that you may be allergic to the allergen that was tested. But the amount of IgE measured doesn't predict how serious your allergy may be.

If the results from either type of test show that you could have an allergy, your provider may refer you to an allergy specialist or recommend a treatment plan. Your treatment plan will depend on what you are allergic to and how serious your symptoms are.

If you're at risk for anaphylactic shock, you'll need to be very careful to avoid the things you are allergic to. You may need to carry an emergency epinephrine treatment (an epinephrine auto-injector) with you at all times. Anaphylactic shock is most common with allergies to certain foods, medicines, insect stings, and latex.

Ask your provider if you are at risk for anaphylactic shock and discuss any questions you have about your test results or your allergy treatment plan.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an allergy blood test?

Allergy blood tests may not always be accurate. Sometimes the results may say you have an allergy when you actually don't (also known as a false positive). This may happen if your body is having a slight reaction to substances in certain foods that you may have eaten before the test. It's uncommon for a blood test to show that you don't have an allergy when you actually do (also known as a false negative).

Depending on your medical history and symptoms, your provider may order an allergy skin test with an allergy blood test, or you may have a skin test alone.

References

  1. American Academy of Allergy Asthma & Immunology [Internet]. Milwaukee (WI): American Academy of Allergy Asthma & Immunology; c2022. Allergy Defined; [cited 2022 Mar 12]; [about 2 screens]. Available from: https://www.aaaai.org/Tools-for-the-Public/Allergy,-Asthma-Immunology-Glossary/Allergy-Defined
  2. Asthma and Allergy Foundation of America [Internet]. Landover (MD): Asthma and Allergy Foundation of America; c1995–2022. Allergies; [reviewed 2015 Sep; cited 2022 Mar 11]; [about 13 screens]. Available from: https://www.aafa.org/allergies/
  3. American College of Allergy Asthma & Immunology [Internet]. American College of Allergy Asthma & Immunology; c2022. Anaphylaxis; [reviewed 2018 Jan 29; cited 2022 Mar 12]; [about 8 screens]. Available from: http://acaai.org/allergies/anaphylaxis
  4. Cleveland Clinic: Health Library: Treatments and Procedures: Allergy Blood Tests [Internet]. Cleveland (OH): Cleveland Clinic; c2022.Bilirubin; [reviewed 2022 Feb 27; cited 2022 Mar 17]; [about 8 screens]. Available from: https://my.clevelandclinic.org/health/treatments/22345-allergy-blood-test
  5. Johns Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; c2022. Allergy Overview; [cited 2022 Mar 12]; [about 3 screens]. Available from: https://www.hopkinsmedicine.org/health/conditions-and-diseases/anaphylaxis
  6. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2022. Diseases and Conditions: Food Allergy; [cited 2022 Mar 11]; [about 9 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/food-allergy/symptoms-causes/syc-20355095
  7. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2022. Diseases and Conditions: Hay Fever; [cited 2022 Mar 11]; [about 10 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/hay-fever/diagnosis-treatment/drc-20373045
  8. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests; [cited 2022 Mar 12]; [about 16 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  9. Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Allergy Blood Testing; [modified 2021 Nov 9; cited 2022 Mar 12]; Available from: https://www.testing.com/tests/allergy-blood-testing/
  10. Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Total IgE; [modified 2021 Nov 9; cited 2022 Mar 12]; [about 9 screens]. Available from: https://www.testing.com/tests/total-ige/
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Allergy Overview; [cited 2022 Mar 12]; [about 8 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P09504

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.