At a Glance
Why Get Tested?
When to Get Tested?
When you have symptoms such as flushing, nausea, throat swelling or low blood pressure that may be due to a life-threatening allergic reaction; when your doctor suspects that you have mastocytosis or mast cell activation
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None, but timing of the sample soon after the beginning of symptoms can be important.
The Test Sample
What is being tested?
This test measures the amount of tryptase in the blood. Tryptase is an enzyme that is released, along with histamine and other chemicals, from mast cells when they are activated, often as part of an allergic immune response.
Mast cells are large tissue cells found throughout the body, but in highest amounts in the skin, in the lining of the intestine and air passages, and also in the bone marrow. Mast cells are part of the body's normal response to injury as well as allergic (hypersensitivity) responses. They contain granules that store a number of chemicals, including tryptase and histamine, that are released when mast cells become activated. In the body, mast cells recognize and bind IgE, a special type of antibody that is often increased in people with allergies and parasitic infections. When IgE that is bound to the surface of mast cells attaches to its target (antigen), mast cells become activated and release their contents. The chemicals released from mast cells (especially histamine) are responsible for many of the symptoms in persons with allergies.
Mast cells contain different forms of the enzyme tryptase, termed alpha (α) and beta (β) tryptase, in both inactive (protryptase) and active forms. In the body, beta tryptase is typically the predominant form of mature tryptase. Testing can be performed to measure total tryptase, which is all of the forms together, or mature tryptase, which measures the mature forms of alpha and beta tryptase. Comparison of the results of these two tests in a total-to-mature ratio may be useful in some instances.
Normally concentrations of tryptase in the blood are very low. When mast cells are activated, levels increase rapidly, rising within 15 to 30 minutes, peaking at 1 to 2 hours, and returning to normal after several hours to a couple of days. In persons with severe allergies, activation of many mast cells can cause a severe form of allergic reaction termed anaphylaxis, which can cause low blood pressure, hives (blisters on the skin), severe narrowing of the air passages, and even death. Tryptase levels will be very high in persons with anaphylaxis.
In some cases, tryptase levels will be high in persons with mast cell activation disorders, in which mast cells become activated without apparent allergies or other reasons.
Tryptase levels can also be significantly and persistently increased with mastocytosis, a rare group of disorders associated with the neoplastic proliferation of mast cells and their infiltration and accumulation in the skin (cutaneous mastocytosis) and/or in organs throughout the body (systemic mastocytosis). Systemic mastocytosis may progress slowly and be relatively slowly progressive or may be aggressive, causing organ dysfunction and, in rare cases, causing a form of leukemia.
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, but timing of the sample soon after the beginning of symptoms can be important. Talk to your doctor about the best time to draw your sample.
Ask a Laboratory Scientist
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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