Allergy Blood Testing

At a Glance

Why Get Tested?

To help diagnose allergies; sometimes to monitor the effectiveness of immunotherapy (desensitization) treatment

When To Get Tested?

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

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

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Looking For Reference Ranges?

You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

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.

Common Questions

How is it used?

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.

When is it ordered?

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:

Hives
Dermatitis
Eczema
Red itchy eyes
Coughing, nasal congestion, sneezing
Asthma
Itching and tingling in the mouth
Throat tightness
Trouble breathing
Abdominal pain or vomiting and diarrhea

A test may also be ordered occasionally to help evaluate the effectiveness of immunotherapy or to determine whether a child has outgrown an allergy.

What does the test result mean?

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.

Is there anything else I should know?

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.

What other tests are available for allergy testing?

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.

My allergy test was negative, but I continue to have symptoms. What else could it be?

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.

My allergy symptoms are generally mild. How serious is this really?

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.

Will my allergies ever go away?

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.

View Sources

Sources Used in Current Review

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(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.

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(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.

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