Immunoglobulin E IgE (Allergy Blood Test)
Immunoglobulin E IgE 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 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:
- 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,
What does the test measure?
The total IgE test measures the quantity of immunoglobulin E (IgE) in the blood. IgE is a type of antibody. Antibodies are proteins that the immune system produces to help defend against potential threats.
The immune system produces IgE antibodies for many specific substances. A total IgE test measures the sum of all these different IgE antibodies in the blood.
Why your child may need an allergen-specific IgE test
Your child’s doctor may order an allergen-specific IgE test if your child has some or all the following symptoms of an allergy:
An allergen-specific IgE blood test may be used in addition to or instead of skin testing. IgE blood tests are often used when children have a skin condition that may interfere with skin testing or cannot stop taking their antihistamines.
Are there different types of allergy blood tests?
There are two types of allergy blood tests:
- Total IgE test: Measures the total amount of IgE in your blood.
- Specific IgE test: Measures the IgE in your blood in response to specific allergens.
What are the indications for IgE testing?
An IgE test is indicated when the taking of a careful patient history and an examination lead to a suspicion of type I allergy.
An IgE test can also be used for monitoring a patient with a known allergic condition, such as:
- Allergic rhinitis (hay fever)
- Allergic conjunctivitis
- Chronic rhinosinusitis.
IgE tests are also useful to determine whether a patient is allergic to a specific protein, such as:
- Types of food allergy (eg, peanuts)
- House dust mites
- Grass, weed or tree pollens
- Animal dander or fur
- Certain drugs and cosmetics
- The venom of a bee or wasp.
An IgE test can be used when skin prick testing is not available or is unsuitable; for example, in an individual with dermo graphism, extensive skin disease, recent use of antihistamines or systemic steroids, or when there is concern that prick testing could cause an anaphylactic reaction.
IgE testing is rarely indicated in atopic dermatitis, allergic contact dermatitis, chronic spontaneous urticaria, or angioedema as the relevance of elevated IgE is uncertain in these diseases.
Which specific allergens can be tested?
The specific allergens that can be tested can be classified as follows :
- Aeroallergens (inhalants)
- Indoor allergens — including house dust mites, animal dander (eg, cat, dog, and cockroach), moulid, and fungal spores
- Outdoor allergens — such as pollens (from grasses, rye, weeds, and trees) and polluted air (smoke)
- Food allergens — including milk, eggs, peanuts, tree nuts, wheat, soy, codfish, and shellfish
- Venoms — including bee, wasp, hornet, ant venoms
- Dust mites (Dermatophagoides)
- Medicines — such as penicillin, aspirin, and others
- Metals (especially nickel, cobalt, chromium, and zinc)
- Household chemicals
IgE tests are also available to test different mixes of allergens. These include a:
- Food mix (ie, egg white, milk, codfish, wheat, peanut, and soybean)
- Cereal mix (ie, wheat, oat, corn, sesame seed, and buckwheat)
- Fruit mix (ie, banana, pear, peach, and apple)
- Seafood mix (ie, codfish, shrimp, mussel, tuna, salmon)
- Grass mix (ie, Bermuda, rye, Timothy, meadow, Johnson, and Bahia grasses)
- Tree mix (ie, olive, willow, eucalyptus, white pine, Melaleuca)
- Nut mix — routine (ie, peanut, hazelnut, brazil nut, almond, and coconut)
- Nut mix — extra (ie, pecan nut, cashew nut, pistachio, and walnut)
- Mould mix (ie, Penicillium, Aspergillus fumigatus, Cladosporium, Candida albicans, and Alternaria).
How do I prepare for an allergy blood test?
You don’t need to do anything special to prepare for an allergy blood test. In some cases, your healthcare provider may want you to fast (not eat or drink) before the test. It’s important to let your provider know if you take antihistamines. They might ask you to stop taking this medication before your test.
What happens during an allergy blood test?
An allergy blood test only takes a few minutes. A healthcare provider called a lab technician usually takes blood samples in your doctor’s office or a lab.
Here’s what you can expect:
- The phlebotomist (a healthcare provider who draws blood) takes blood from a vein in your arm using a thin needle.
- The needle might cause a mild pinch and some discomfort.
- The phlebotomist fills a collection tube with blood and then removes the needle.
- They place a small bandage on your arm.
Table. IgE level test ratings and interpretations:
|Rating of specific IgE level (kUA/L)||Grade/Class||Interpretation|
|Absent or undetectable (< 0.35)||0||Unlikely|
|Low (0.35–0.69)||I||Doubtful significance|
|High (3.50–17.49)||III||More possible|
|Very high (17.50–49.99)||IV||More likely|
|Very high (50.00–100.00)||V||Very likely|
|Extremely high (> 100.00)||VI||Extremely likely|
What happens during an allergy blood test?
A healthcare 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.
Before the test
There are no special preparations or precautions to take prior to a total IgE blood test.
During the test
During a total IgE test, a small needle is placed into your vein. Beforehand, a health professional may tie an elastic band around your upper arm. They will also clean part of your skin with an antiseptic.
After the needle is inserted into your vein, blood is withdrawn into a vial or test tube. You may feel a slight sting when the needle is inserted. The test itself usually takes less than five minutes to complete.
After the test
Once the test is over, you can resume all normal activities. There are very few risks associated with a total IgE blood test. You may have some slight discomfort or bruising in your arm, but this typically resolves quickly.
Receiving test results
Results from your total IgE test are usually available within a few business days after the laboratory receives your blood sample. Results may be provided directly by your doctor, and you may also get a test report by mail or electronically.
Interpreting test results
Your total IgE test results show the amount of immunoglobulin E in your blood. Test results are displayed as international units per milliliter of blood (IU/mL) or nanograms per milliliter of blood (ng/mL).
Laboratory results usually display your test result along with a reference range. Reference ranges are based on test results from large groups of people. These ranges help outline the expected total IgE levels in healthy people.
Your test results are interpreted in the context of your overall health, including any symptoms that you may have. Total IgE levels may help identify certain conditions, but this test alone is rarely able to make a diagnosis. For this reason, the meaning of your test results should always be explained by your doctor.
Elevated levels of total IgE can be caused by a number of medical conditions including parasitic infections, some allergies and asthma, certain immune disorders, and some types of cancer. Additional tests are typically necessary to determine the underlying cause.
It is also possible to have very low levels of total IgE as a result of some types of diseases that cause abnormal immune function.
Are test results accurate?
Laboratory methods can typically measure total IgE levels accurately. However, no test is perfectly accurate. In addition, because multiple factors can affect IgE levels, the test alone may not clearly identify any specific medical condition.
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.
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.