Allergies

How is Allergy Blood Test Done?

An allergy blood test is used to determine allergy. This test involves taking a blood sample from the patient and testing it for IgE antibodies. IgE antibodies are released in an allergic reaction. If these antibodies are present in the blood sample, the person is diagnosed as having an allergy.

How Does Allergy Blood Test Determine Allergy?

An allergy is caused when the immune system mistakenly identifies certain substances as allergic and reacts against it. Such substances are known as allergens.

When the immune system encounters an allergen, it releases IgE antibodies to fight it. Now the person is said to be sensitized to the allergen. The next time he/she encounters an allergen, the IgE binds itself to the allergen. The IgE also attaches to the mast cells and triggers the release of histamine. The release of histamine initiates the allergic reaction. Hence, high IgE antibody levels in the blood would indicate an allergy.

For the testing of allergies, skin prick test is recommended. However, allergy blood test is recommended if:

  • If the individual is taking anti-histamines, as they can interfere with  the skin test
  • If the individual is having eczema or other skin disease which can interfere with skin test
  • If the doctor suspects severe skin reaction with the skin prick test

How is Allergy Blood Test Done?

A blood sample is taken from the patient. This sample is tested in the lab for IgE antibody levels for specific allergens. High amount of IgE antibodies in the blood against a specific allergen indicates the presence of an allergy.

A positive test shows that you are having an allergy, whereas a negative test shows that you may not have allergies.

An example of allergy blood test is the radioallergosorbent test (RAST) test , which is test for allergies. As a positive blood test may not completely determine allergy, your doctor may analyze signs and symptoms or recommend further allergy tests.
To determine your allergy profile – blood test is helpful, as it can help determining the antibodies produced against specific allergens. Consult your allergist if you would like to take up this test.

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