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Why is the Tryptase Blood Test Ordered?
The tryptase blood test is usually ordered by the doctor to confirm a diagnose of anaphylaxis or mastocytosis. Anaphylaxis is an allergic reaction that makes breathing difficult, lowers blood pressure, and causes hives to develop on the skin. Mastocytosis is a condition characterized by an overproduction of mast cells, which causes fatigue, skin lesions, and abdominal discomfort.
Usually, the presence of recurrent symptoms that resemble anaphylaxis and the absence of a known cause will prompt a doctor to check the tryptase level. For example, if you have a swollen face, throat, or tongue, experience flushing, or have itchy skin, but don't have a known food allergy, such as peanuts, or a known allergy to insect bites, such as bee stings, then the doctor will order a tryptase blood test.
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What Does the Test Measure?
The tryptase blood test measures the amount of tryptase in the blood. Tryptase is an enzyme that is released from mast cells during an allergic immune response. The test is a good way to see how well the mast cells are functioning.
Mast cells release two types of tryptase enzymes, alpha and beta, in both an activated form and inactivated form. The tryptase test can measure the total tryptase level, which includes all four forms, or it can measure just the activated forms. A ratio of the total tryptase level to the activated forms is usually used to distinguish between anaphylaxis and mastocytosis.
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How is the Test Performed?
The tryptase blood test requires a sample of blood drawn from a vein in the arm using a syringe needle. The time at which the blood sample is taken, relative to the onset of symptoms, is important. The level of tryptase in the blood changes after mast cells are activated. Within 15 to 30 minutes of activation, the level of tryptase in the blood increases, and it generally peaks after 1-2 hours. The level subsides to normal levels after several hours. If the blood sample is taken too early or too late, the results may not indicate an abnormal tryptase level.
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Tryptase Blood Test Results
A blood tryptase level that suddenly becomes high and then dissipates indicates that the symptoms are due to anaphylaxis. If the tryptase level is elevated for a long period of time and doesn't return to a normal baseline, then the symptoms are most likely due to mastocytosis. If the ratio of total tryptase to the activated form of tryptase is less than 10, then the symptoms are most likely due to anaphylaxis. If the ratio is greater than 20, then the symptoms are most likely a result of systemic mastocytosis.
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1. "Tryptase." Lab Tests Online. American Association for Clinical Chemistry. 24 Nov. 2010. Web. 8 Dec. 2010.
2. Schwartz, Lawrence B. "Tryptase Levels as an Indicator of Mast-Cell Activation in Systemic Anaphylaxis and Mastocytosis." The New England Journal of Medicine. 25 Jun. 1987. Web. 8 Dec. 2010.