Tryptase is an enzyme released primarily by mast cells, which are a type of immune system cell found throughout the body. When mast cells become activated, they release various chemicals, including tryptase, into the bloodstream. Measuring the level of tryptase in the blood can provide important information about mast cell activity, serving as a biomarker that may indicate several underlying health conditions.
What is Tryptase and How It’s Measured
Tryptase is a serine protease enzyme stored within mast cells, which are abundant in tissues like the skin, airways, and digestive system. When activated, mast cells rapidly release their contents, including tryptase and histamine, contributing to immune responses and inflammation.
A tryptase test measures the amount of tryptase released into the blood, typically using a serum sample, to assess mast cell activity. Normal baseline levels of total tryptase in healthy adults range from 1 to 15 ng/mL. This range accounts for physiological variations, including hereditary alpha-tryptasemia.
Acute Causes of Elevated Tryptase
Tryptase levels can increase rapidly and temporarily due to acute mast cell activation. The most recognized acute cause is anaphylaxis, a severe, potentially life-threatening allergic reaction. During anaphylaxis, mast cells degranulate extensively, releasing significant tryptase into the bloodstream.
Following an anaphylactic event, serum tryptase levels typically rise within 15 to 30 minutes, peaking 1 to 2 hours after symptom onset. These elevated levels remain detectable for several hours, generally returning to baseline within 12 to 24 hours due to tryptase’s two-hour half-life.
While anaphylaxis is a primary cause, other acute scenarios involving widespread mast cell activation, such as severe drug reactions, trauma, or sepsis, can also lead to transient tryptase elevations.
Chronic Causes of Elevated Tryptase
Persistently elevated tryptase levels often indicate chronic conditions involving mast cells. Mastocytosis is a primary cause, characterized by an abnormal increase of mast cells in various body tissues. Systemic mastocytosis, where mast cells proliferate in organs beyond the skin, is frequently associated with elevated baseline tryptase levels, often exceeding 20 ng/mL. Cutaneous mastocytosis, primarily affecting the skin, typically has normal or only slightly elevated tryptase.
Another common cause for chronically increased tryptase is Hereditary Alpha-Tryptasemia Syndrome (HATS). This genetic trait involves extra copies of the TPSAB1 gene, leading to constitutively higher baseline tryptase concentrations. HATS affects about 5% of the population, often resulting in baseline levels above 8 ng/mL without mast cell proliferation.
Certain myeloid neoplasms, types of blood cancers, can also be associated with elevated tryptase, especially if they involve mast cell proliferation or abnormal myeloid cell growth. Impaired kidney function can also lead to moderately elevated tryptase levels, as kidneys clear tryptase from the body.
Interpreting Tryptase Levels and Diagnostic Significance
Interpreting tryptase levels requires careful consideration, distinguishing between acute and baseline measurements. For suspected acute events like anaphylaxis, blood samples are ideally collected within 1 to 2 hours of symptom onset, followed by a second sample at least 24 hours later to establish the individual’s baseline. This comparison confirms significant mast cell activation during the event.
An elevated tryptase level marks mast cell activity but is not a standalone diagnosis. While a significant rise during an acute event strongly supports anaphylaxis, normal levels do not definitively rule it out, especially in some food-induced reactions.
For chronic elevations, a persistently high baseline tryptase level above 20 ng/mL is a minor criterion for diagnosing systemic mastocytosis. Further medical evaluation, including bone marrow biopsies or genetic analysis, is needed to determine the underlying cause and guide management.