Allergy Blood Test
Reviewed
Also called: IgE allergy test, Quantitative IgE, Immunoglobulin E, Total IgE, Specific IgE, Allergy Screen
An allergy blood test measures the amount of allergy-causing antibodies called immunoglobulin E (IgE).
Specimen: Blood
Why this test may be ordered
- Symptoms of allergy: stuffy or runny nose, sneezing, itchy/watery eyes, hives, diarrhea, vomiting, shortness of breath, coughing, wheezing.
- If you cannot have allergy skin testing due to skin conditions, certain medicines, or risk of serious allergic reaction.
- Sometimes for young children because skin testing may be too uncomfortable.
Preparation and collection
You don't need any special preparations for an allergy blood test. You may need to stop taking certain medicines before this test, such as antihistamines, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.
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.
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.
Understanding results
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).
- High total IgE: A total IgE test result that is high means that you may have some kind of allergy. Limitation: But the results of a total IgE test don't show what you're allergic to or how serious your allergy may be. Higher amounts of IgE may also be caused by smoking or a parasitic infection. Next step: 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.
- High specific IgE for a tested allergen: A specific IgE test result that is high means that you may be allergic to the allergen that was tested. Limitation: But the amount of IgE measured doesn't predict how serious your allergy may be. Next step: 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.
- Physical risks: minimal; slight pain or bruising at needle site; most symptoms go away quickly.
- False-positive: sometimes results may say you have an allergy when you do not; this may happen if your body has a slight reaction to substances in certain foods that you may have eaten before the test.
- False-negative: it is uncommon for a blood test to show you do not have an allergy when you actually do.
- Total IgE test does not show what you are allergic to or how serious your allergy may be.
- Specific IgE test amount does not predict how serious your allergy may be.
What to do next
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. 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.
- 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.
- What do my test results mean in the context of my symptoms?
- Do I need any additional testing, such as a skin test?
- Should I stop taking any medications before the test?
- How accurate are allergy blood tests?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.