To help diagnose allergies; sometimes to monitor the effectiveness of immunotherapy (desensitization) treatment
When you have symptoms such as hives, dermatitis, nasal congestion, red itchy eyes, asthma, or abdominal pain that your healthcare practitioner suspects may be caused by an allergy
A blood sample drawn from a vein in your arm
Immunoglobulin E (IgE) is a class of antibody (immune protein) associated with allergic reactions. It is normally found in very small amounts in the blood. This test measures the amount of allergen-specific IgE in the blood in order to detect an allergy to a particular substance.
IgE is an antibody that functions as part of the body's immune system, its defense against "intruders." When someone with a predisposition to allergies is exposed to a potential allergen such as food, grass, or animal dander for the first time, that person becomes sensitized. The person's body perceives the potential allergen as a foreign substance and produces a specific IgE antibody that binds to specialized mast cells in the skin, respiratory system, and gastrointestinal tract, as well as to basophils (a type of white blood cell) in the bloodstream. With the next exposure, these attached IgE antibodies recognize the allergen and cause the mast and basophil cells to release histamine and other chemicals, resulting in an allergic reaction that begins at the exposure site.
A total IgE test measures the overall number of IgE antibodies in the blood, while a specific IgE test measures for a response to individual allergens. Each allergen-specific IgE antibody test performed is separate and very specific; for example, it will test honeybee versus bumblebee, egg white versus egg yolk, and giant ragweed versus western ragweed. Groupings of these tests, such as food panels or regional weed, grass, and mold panels, can be done. Alternatively, the healthcare practitioner may pick and choose selectively from a long list of individual allergens suspected of causing a person's allergies.
While the traditional method for blood testing was the RAST (radioallergosorbent test), it has been largely replaced with newer IgE-specific immunoassay methods. Some healthcare practitioners continue to refer to all IgE allergy blood tests as RAST even though it is not the exact assay that the testing laboratory uses.
The allergen-specific IgE antibody test is a blood test used to help diagnose an allergy to a specific substance or substances for a person who presents with acute or chronic allergy-like symptoms. This is especially true if symptoms are recurrent and appear to be tied to triggers, such as exposures to particular foods or environments, and if other family members are known to have allergies.
Other types of allergy tests may be performed by exposing a person to different substances under careful medical supervision. The usefulness of these tests, however, can be affected by skin conditions, such as significant dermatitis or eczema, and by medications, such as antihistamines and some antidepressants. With some tests there is also the potential for severe reactions, including, for example, anaphylaxis, which can be life-threatening. In these cases, the allergen-specific IgE antibody test may be ordered as an alternative, as it is performed on a blood sample.
The allergen-specific IgE antibody test may also be performed to monitor immunotherapy (desensitization) or to see if a child has outgrown an allergy. Typically, the healthcare practitioner will interpret the results of the test in comparison with a person's symptoms and any other allergy tests being performed.
One or more allergen-specific IgE antibody tests may be ordered when a person has signs or symptoms that suggest an allergy to one or more substances. Signs and symptoms may include:
A test may also be ordered occasionally to help evaluate the effectiveness of immunotherapy or to determine whether a child has outgrown an allergy.
An elevated allergen-specific IgE result indicates that the person tested likely has an allergy. However, the amount of specific IgE present does not necessarily predict the potential severity of a reaction. A person's clinical history and additional medically-supervised allergy tests may be necessary to confirm an allergy diagnosis.
Negative results indicate that a person probably does not have a "true allergy," an IgE-mediated response to the specific allergens tested.
Results of allergy blood testing must be interpreted with care. False negatives and false positives can occur. Even if an IgE test is negative, there is still a small chance that a person does have an allergy. Similarly, if the specific IgE test is positive, a person may or may not ever have an actual physical allergic reaction when exposed to that substance.
Sometimes, a healthcare practitioner will look at other blood tests for an indirect indication of an ongoing allergic process, including a total IgE level or a complete blood count (CBC) and white blood cell differential (specifically eosinophils and basophils). Increases in these test results may suggest an allergy, but they may also be elevated for other reasons.
Skin prick or scratch tests, intradermal tests, patch tests, and oral food challenges are usually performed by an allergist or dermatologist. These tests can be subjective and depend on factors such as dose of allergens, administration of the tests, and interpretation of results.
Your healthcare provider may also try eliminating foods from your diet and then reintroducing them to find out what you are allergic to. It is important that these tests be done under close medical supervision, as a life-threatening anaphylactic reaction is possible.
You could have an allergy-like condition that is not mediated by IgE for which there are no specific laboratory tests. You might have a genetic hypersensitivity problem, such as sensitivity to gluten with celiac disease or have an enzyme deficiency, such as a lactase deficiency causing lactose intolerance. It could also be another disease that is causing allergy-like symptoms. It is important to investigate your individual situation with your healthcare provider's assistance. Test results alone cannot diagnose allergies, but rather confirm a diagnosis when circumstances suggest an allergy is likely. Results from any type of allergy test have to be interpreted along with your medical history by a healthcare practitioner who is trained to diagnose allergies specifically.
Allergic reactions are very individual. They can be mild or severe, vary from exposure to exposure, get worse over time (or may not), involve the whole body, and can sometimes be fatal.
Although children do outgrow some allergies, adults usually do not. Allergies that cause the worst reactions, such as anaphylaxis caused by peanuts, do not usually go away. Avoidance of the allergen and advance preparation for accidental exposure, in the form of medications such as antihistamines and portable epinephrine injections, is the safest course. Immunotherapy can help decrease symptoms for some unavoidable allergies but won't work for food and the treatment, which usually consists of years of regular injections, may need to be continued indefinitely.
Sources Used in Current Review
Allergy Testing. American College of Allergy, Asthma & Immunology. Available online at https://acaai.org/allergies/treatment/allergy-testing. Accessed 3/7/2018.
(September 2011) Allergy blood testing: A practical guide for clinicians. Cleveland Clinic Journal of Medicine. Available online at https://www.mdedge.com/ccjm/article/95541/immunology/allergy-blood-testing-practical-guide-clinicians. Accessed 3/7/2018.
(July 2014) Blood Test: Allergen-Specific Immunoglobulin E (IgE). KidsHealth from Nemours. Available online at https://kidshealth.org/en/parents/test-ige.html. Accessed on 3/7/2018.
Allergy Blood Test. MedlinePlus. Available online at https://medlineplus.gov/labtests/allergybloodtest.html. Accessed 3/7/2018.
(January 16, 2018) Allergy Skin Tests. Mayo Clinic. Available online at https://www.mayoclinic.org/tests-procedures/allergy-tests/about/pac-20392895. Accessed 3/7/2018.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Sicherer, S. (1999, January 15). Manifestations of Food Allergy: Evaluation and Management. American Family Physician [On-line serial]. Available online at http://www.aafp.org/afp/990115ap/415.html.
American Academy of Family Physicians (1999, January 15). Food Allergies: Just the Facts. American Family Physician [On-line serial]. Available online at http://www.aafp.org/afp/990115ap/990115f.html.
ARUP. Immunoglobulin E. Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_ijk4.htm.
Sicherer, S. (2001, April 5th last update). Food Allergy Testing: Questions and Answers. Food Allergy News Reprint [On-line information]. Available online at http://www.foodallergy.org/topics_archive/testing.html.
Formanek, R. (2001, July-August). Food Allergies: When Food Becomes the Enemy. U.S. Food and Drug Administration, FDA Consumer magazine [On-line serial]. Available online at http://www.fda.gov/fdac/features/2001/401_food.html.
MEDLINEplus (2002, January 2, Updated). Allergies. MedlinePlusHealth Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000812.htm.
MEDLINEplus (2002, January 2, Updated). Allergy testing. MedlinePlusHealth Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003519.htm.
WAO [2000-2002]. Overview of Allergy, Its Diagnosis and Treatment. World Allergy Organization [On-line information]. Available online at http://www.worldallergy.org/public/descriptions_of_allergies/overview.shtml.
National Institute of Allergy and Infectious Disease (1998 February). Something in the Air: Airborne Allergens. WebMD [On-line serial]. Available online at http://my.webmd.com/content/article/1680.50308.
National Institute of Allergy and Infectious Diseases (1999 January, last revision). Food Allergy and Intolerances. WebMD [On-line serial]. Available online at http://my.webmd.com/content/article/1680.50303.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 38-44.
(© 2010). Tips to Remember: Allergic Reactions. American Academy of Allergy Asthma and Immunology, [On-line information]. Available online at http://www.aaaai.org/patients/publicedmat/tips/whatisallergicreaction.stm. Accessed February 2010.
(© 2010). Tips to Remember: Asthma & Allergy Medications. American Academy of Allergy Asthma and Immunology [On-line information]. Available online at http://www.aaaai.org/patients/publicedmat/tips/asthmaallergymedications.stm. Accessed February 2010.
Mayo Clinic Staff (2009 June 24). Allergy medications: Know your options. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/allergy-medications/AA00037/METHOD=print. Accessed February 2010.
Hinshaw, W. D. et. al. (Updated 2009 June 02). Hypersensitivity Reactions, Delayed. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/136118-overview. Accessed February 2010.
Anand, M. and Routes, J. (Updated 2009 June 16).Hypersensitivity Reactions, Immediate. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/136217-overview. Accessed February 2010.
Mayo Clinic Staff (2009 April 03). Allergy Skin Tests. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/allergy-tests/MY00131/METHOD=print. Accessed February 2010.
(© 2009). Tips to Remember: What is Allergy Testing? American Academy of Allergy Asthma and Immunology, [On-line information]. Available online at http://www.aaaai.org/patients/publicedmat/tips/whatisallergytesting.stm. Accessed February 2010.
Zieve, David. (Updated 2012). Allergy testing – skin. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003519.htm through http://www.nlm.nih.gov. Accessed October 2013.
American Academy of Allergy Asthma & Immunology. (Updated 2013). Allergic Reactions: Tips to Remember. Available online at http://www.aaaai.org/conditions-and-treatments/library/at-a-glance/allergic-reactions.aspx. Accessed October 2013.
American Academy of Allergy Asthma & Immunology (@2010). Allergy Testing. Available online at http://www.acaai.org/allergist/allergies/treatment/diagnosing-allergies/pages/allergy-testing.aspx. Accessed October 2013.
Fischbach, F.T. (2004). A Manual of Laboratory & Diagnostic Tests. 7th Edition., Lippincott Williams & Wilkins, Philadelphia.
(Updated Jan 17, 2014) Diaz R. Diagnostic Allergy Testing. Medscape Reference. Availalble online at http://emedicine.medscape.com/article/2068676-overview#a1. Accessed January 2014.
(March 2008) Bernstein L, et al. Allergy Diagnostic Testing: An Updated Practice Parameter. Annals of Allergy, Asthma and Immunology. March 2008; Volume 100, Number 3, Supplement 3.
(July 18, 2012) National Institute of Allergy and Infectious Diseases. What Makes and Allergen an Allergen. Available online at http://www.niaid.nih.gov/topics/allergicDiseases/research/Pages/whatMakesAllergens.aspx. Accessed January 2014.