Blood Tests

Allergy blood tests measure the presence of IgE antibodies to specific foods. (IgE, short for “immunoglobulin E,” is the antibody that triggers food allergy symptoms.) In the past, these tests were called “RASTs” (which stands for radioallergosorbent tests) because they used radioactivity, but modern tests do not. 

What is allergy blood testing?

Allergy blood testing, also known as sIgE (specific immunoglobulin E) testing, uses one small blood sample to measure the amount of allergen-specific IgE antibodies in the blood.¹ The test can look at many possible allergens to determine if you’re sensitized (have specific IgE) to any of those allergens, including pollens, molds, foods, and animal dander.  

What is the difference between blood tests and skin prick tests?

Both the blood test and skin prick tests (SPTs) detect allergen-specific IgE. With the skin tests, the result is immediately available in the office. Blood tests must be sent to a lab and results take several days or longer to arrive for review by your healthcare provider.  

Unlike the skin prick test, the blood test is not affected by antihistamines such as Benadryl and can be performed on people with extensive rash. 

What allergies can blood tests be used to test for?

Allergy blood tests are commonly used to identify sensitization to foods, pollens, molds, animal dander, dust mites, insect venoms, and some medications.  

When should you get a food allergy blood test?

You should only request a test if you have experienced food allergy symptoms. Food allergy blood test results must be considered along with your medical history and a physical examination by a healthcare professional who can determine whether you have a clinical food allergy. Blood testing or skin prick testing alone does not confirm a food allergy diagnosis.

Once you have a food allergy diagnosis that is confirmed by a healthcare provider, an appropriate and personalized treatment plan can be recommended. 

What are the symptoms that show you might have a food allergy?

You should only request a food allergy blood test for specific foods that seem to be causing consistent allergic symptoms. Symptoms of a possible food allergy include:

• Skin symptoms: Hives, itching, flushing, or swelling, especially of the face, lips, tongue, and eyelids
• Mouth and throat symptoms: Itching or tingling in the mouth, swelling of the throat, hoarseness, or a change in voice
• Nose and nasal symptoms: Runny nose, nasal congestion, sneezing, or a metallic taste
• Lungs and chest symptoms: Wheezing, coughing, chest tightness, or difficulty breathing
• Stomach symptoms: Abdominal pain, cramps, diarrhea, nausea, or vomiting
• Head symptoms: Dizziness, lightheadedness, or fainting
• Heart symptoms: Changes in heart rate, weakness, or low blood pressure
• Nervous system symptoms: Anxiety, confusion, or a sense of impending doom 

Who can order a food allergy blood test?

Any healthcare provider that can order laboratory testing (including primary care providers) can order food allergy blood tests. However, food allergy blood testing should only be done when a person’s clinical history shows that a food allergy is suspected. Random testing using large allergen panels is not recommended because it can be expensive and has a high likelihood of false positive results.  

What are the benefits of food allergy blood testing?

Blood tests are easy, safe, and accessible. Allergy blood tests only require a blood draw. If you’re experiencing food allergy symptoms, you can request allergy blood testing from any healthcare provider that normally orders laboratory testing. You can receive a test regardless of your age, skin condition, antihistamine use, and pregnancy status.^3,4  

Blood tests are helpful in making a food allergy diagnosis. Blood allergy testing is considered as effective as skin-prick testing and, most often, these tests are used in conjunction. Blood tests can help identify specific allergens that may be triggering your symptoms. For food allergy, an additional test called an oral food challenge (OFC) is often needed to fully confirm an actual food allergy. This procedure is performed under medical supervision, in a clinic equipped to treat both mild and more serious allergic reactions, should one occur.  

A food allergy blood allergy test can be interpreted by any healthcare provider.² If a food allergy is confirmed, your healthcare provider can prescribe the appropriate medications, such as antihistamines and emergency treatments (epinephrine), provide guidance on food allergy management, and refer you to an allergist who can review the results of the blood allergy testing and discuss options for long-term management and treatment.

How do you understand food allergy blood testing results?

Different laboratories can use different “brands” of the blood test that may report results using different scoring systems or units. Your healthcare provider or allergist must be aware of these differences because the tests and reporting systems are not interchangeable.

Your healthcare provider or allergist should explain the meaning of the blood tests to you. The results are NOT helpful for predicting the severity of a food allergy. Instead, the test gives information about the chance that you have a food allergy. (This test is not like a pregnancy test, in which a person “is” or “is not” pregnant.)

How much does a food allergy blood test cost?  

The cost for a food allergy blood test depends on a few factors—it’s not super cut and dry. Factors include how many allergens are being tested, your health insurance coverage, and the lab doing the test.  

Most health insurance plans, including Medicare and Medicaid, cover food allergy blood testing. As mentioned above, getting a large panel of allergy tests without any evidence of a possible food allergy is not advised and can be expensive.

For more specific cost information, contact your insurance company, or contact your provider for associated costs and options. 

"False Positive" Results

Both food allergy blood tests for skin prick tests can produce false positive results. This means that the test indicates an allergy even though the person is not actually allergic. Some studies show half of these tests can show a false positive. There are two reasons these tests can show a false positive: 

• Nonspecific binding: The test may be detecting proteins that are similar to the food being tested, but do not cause an allergic reaction. For example, a person who is allergic to peanuts may also test positive for other legumes, like green beans. 
• Undigested food proteins: The test may be measuring the body's response to undigested food proteins. 

Any positive food allergy blood test result must be confirmed by a history of allergic symptoms. 

References

¹_{Siles RI, Hsieh FH. Allergy blood testing: A practical guide for clinicians. Cleve Clin J Med. 2011 Sep;78(9):585-92. doi: 10.3949/ccjm.78a.11023. PMID: 21885690.Bonnelykke K, Pipper CB, Bisgaard H. J Allergy Clin Immunol. 2008;121(3):646-651.}

²_{Lu, Y. Z., & Kwong, K. Y. C. (2024). A comparison of healthcare utilization and outcomes following skin vs. serum-specific IgE allergy testing. Journal of Medical Economics, 27(1), 730–737. https://doi.org/10.1080/13696998.2024.2349471}

³_{Pali-Schöll I, Namazy J, Jensen-Jarolim E. Allergic diseases and asthma in pregnancy, a secondary publication. World Allergy Organ J. 2017 Mar 2;10(1):10. doi: 10.1186/s40413-017-0141-8. PMID: 28286601; PMCID: PMC5333384.}

⁴_{A WAO - ARIA - GA²LEN consensus document on molecular-based allergy diagnostics.  Canonica, Giorgio Walter et al.  World Allergy Organization Journal, Volume 6, 17.} 

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