Allergy Blood Test (IgE)

Allergy Blood Test (IgE); types, preparations & results interpretation

Allergy Blood Test (IgE) or immunoglobulin E; What is this test used for, what are its different types, and what are the indications of its results?

Allergy blood test, also known as a serum Ige blood test, test is a blood test and an effective allergy diagnostic tool that determines the concentration of specific IgE antibodies in the blood. It can test for hundreds of allergy triggers, including pollen, mould, food allergy, and animal dander.

What is allergy blood test?

Allergy blood tests detect and measure antibodies known as immunoglobulin E (IgE). Antibodies are proteins produced by your immune system in response to potentially harmful substances such as viruses or bacteria.

Allergy symptoms vary according to the type of allergy you have. They can range from itching and sneezing to asthma or a potentially fatal condition known as anaphylactic shock.

Even if the allergen is harmless, your body produces IgE in response to it if you have an allergy. Some common allergens are:

  • Some foods or ingredients.
  • Dust.
  • Latex.
  • Insect stings and bites
  • Mold.
  • Dander from pets.
  • Pollen.
  • Some medicines.

This type of allergy test was previously known as rast radioallergosorbent test (RAST) because it used radioactivity, but it no longer does.

Brief Description for allergy testing (IgE)

Other names IgE allergy test, Immunoglobulin E, Total IgE, Specific IgE, RAST, CAP, ELISA, Quantitative IgE.
Test purpose To help in allergy diagnosis
specimen Serum
preparation None
Reference Range Less than 0.10 kU/L
Methodology Flourescent Enzyme Immunoassay

Different types of allergy blood tests

There are two kinds of allergy blood tests:

  1. The total IgE test is a blood test that measures the total IgE antibodies in your blood.
  2. A specific IgE test: blood tests can screen allergen-specific antibodies in your blood produced by your body in response to a single allergen. Each allergen that may be causing your allergies is tested separately.

When is a blood allergy test required?

Allergy blood testing is used to diagnose an allergy. If you have any of the following symptoms, you may require an allergy blood test:

  • Allergic rhinitis (hay fever), is usually caused by pollen, pet allergies, or mold (aspergillosis).
  • Anaphylaxis is a severe and sometimes fatal allergic reaction to specific foods, insect stings, or other allergens.
  • Contact dermatitis is a skin condition caused by coming into contact with irritants such as chemicals, detergents, poisonous plants, or certain metals (such as a nickel allergy).

Among the allergy symptoms are:

  • Lips, tongue, eyes, or face swelling.
  • Runny or stuffy nose.
  • Sneezing.
  • Watery, itchy eyes.
  • Hives (itchy raised red patches on the skin).
  • Diarrhea.
  • Vomiting.
  • Breathing difficulty.
  • Throat discomfort (pharyngitis).
  • Coughing.
  • Wheezing.
  • Eczema.
  • Headache.

Why was RAST chosen over a skin test?

The typical way for doctors to test for allergies is through skin prick testing. Skin testing involves putting allergens directly on or into your skin, but blood testing involves drawing blood samples, and it may ordered in some cases if allergy skin testing is not possible.

You may not be able to have skin testing or Allergy blood testing is recommended if you:

  • Have an extreme reaction to skin testing or a history of a potentially fatal allergic reaction known as anaphylaxis.
  • Have specific skin conditions.
  • Take any medications that may have an impact on the test results.
  • Cannot stand the numerous needle scratches required for skin testing.
  • Have a heart condition that is unstable.
  • Have asthma that is poorly controlled.
  • Have severe eczema, dermatitis, psoriasis, or another form of severe skin disease.

Your doctor may also order blood tests to determine the effectiveness of your allergy treatments (immunotherapy). Blood tests can also determine whether you have outgrown an allergy.

Preparations for allergy blood test (IgE)

Allergy Blood Test
Immunoglobulin E test

There is no need for you to do anything special to prepare for an allergy blood test. In some cases, It is critical to inform your provider if you use antihistamines. They may request that you discontinue taking this medication prior to your test.

What happens during IgE test?

An allergy blood test is a laboratory test performed on blood. it takes only a few minutes.
A thin needle is used to draw blood from a vein in your arm. The needle may cause a minor pinch and discomfort. The phlebotomist draws blood into a collection tube and then removes the needle.

Results Interpretation

Every person has some IgE in of there blood, but elevated levels indicate that you may be allergic to something. However, the results of a total rast test do not reveal what you are allergic to or how severe your allergy may be.

  • A positive ige blood tests result indicates that you may be allergic to the allergen tested. However, the amount of IgE measured does not predict the severity of your allergy.

If the results of either type of test indicate that you may be allergic to something, your provider may refer you to an allergy specialist or recommend a treatment plan. Your treatment plan will be determined by what you are allergic to and the severity of your symptoms.

  • A negative result indicates that you do not have a true allergy. That means your immune system is most likely not reacting to the allergen tested.

Reference Range


(reported in kU/L)

IgE Mediated Probability

Clinical Response

Less than 0.10 No significant level detected
0.10 – 0.34 Clinical relevance undetermined
0.35 – 0.70 Low
0.71 – 3.50 Moderate
3.51 – 17.50 High
17.51 – 50.00 Very high
50.01 – 100.00 Very high
Greater than 100.00 Very high


And finally, Allergy blood tests are not always reliable. The results may indicate that you have an allergy when you do not (also known as a false positive). This could happen if your body is having a minor reaction to substances in foods you ate before the test. It is unusual for a blood test to show that you do not have an allergy when you do (also known as a false negative).

Based on your medical condition and symptoms, your doctor may request an allergy skin test in conjunction with an allergy blood test, or a skin test only.

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