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The Test Sample
What is being tested?
Immunoglobulin E (IgE) is an antibody that is produced by the body’s immune system in response to a perceived threat. It is one of five classes of immunoglobulins (A, G, M, D, and E) and is normally present in the blood in very small amounts. This test measures the amount of IgE in the blood.
Immunoglobulins are proteins that play a key role in the body's immune system. They are produced by specific immune cells called plasma cells. Immunoglobulins are produced in response to bacteria, viruses, and other microorganisms as well as substances that are recognized as "non-self" or present harmful antigens to the immune system.
Immunoglobulin E is associated with allergic responses, including asthma, and to a lesser degree with immunity to parasites. With allergies, the body overreacts to one or more substances in the environment called allergens that do not typically cause a response in other people. Someone may develop an allergy when that person is exposed to an allergen, such as plant pollen, peanuts, eggs, strawberries, bee venom, and hundreds of other potential substances.
During an initial exposure, also called sensitization, an allergic person produces an IgE specifically directed against that allergen. IgE binds to specialized white blood cells, resulting in the release of a number of substances, including histamine. In allergic/asthmatic people, this can cause constriction of the bronchi in the lungs. These substances are also responsible for the running nose, itchy eyes, and skin itching that occur in people with allergies.
Each time an allergic person is exposed to a specific allergen(s) after the initial exposure, IgE is rapidly produced, increasing to levels that trigger an allergic reaction. The severity of the reaction and symptoms associated with each episode can range from a localized reddening and itching of the skin, to respiratory distress, to vomiting and diarrhea, and in some cases to life-threatening anaphylaxis. Severity will vary from person to person, can vary from episode to episode, and may worsen over time.
The total IgE test measures the overall quantity of immunoglobulin E in the blood, not the amount of a specific type. It can be used to detect an allergic response in the body rather than a specific allergy. This test may compliment the information provided by allergy tests that detect allergen-specific IgE.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.