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Blood Test Tracker

Tryptase

Measures tryptase, a protein mast cells release in allergic reactions. It is checked after a possible severe reaction and to find your usual baseline level.

AI-verified against cited sources. Awaiting expert reviewAlso called MCT, bSTLOINC 21582-2

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What it is

Tryptase is a protein stored in mast cells, immune cells that release chemicals during allergic reactions. A small amount is always in the blood, and this usual level reflects how many mast cells you have. During a severe allergic reaction such as anaphylaxis, mast cells release much more, so the level rises for a few hours. This test measures total tryptase. It does not separate the different types of tryptase.

Why it matters

Clinicians use two kinds of tryptase results. A sample taken within a few hours of a reaction can show whether mast cells released their contents. A baseline sample taken at least 24 hours after you have recovered shows your usual level. A higher usual level is linked to more severe reactions to insect stings, and it can point toward an inherited trait that is fairly common and often causes no problems, or less often toward a mast cell condition. A result in the usual range does not rule out an allergic reaction.

If it’s high

A level above your lab's range can mean different things depending on when the blood was drawn. Within a few hours of a reaction, a high level suggests that mast cells released their contents. At baseline, a high level is more often due to an inherited trait or other health factors than to a mast cell disease. The number alone cannot tell the cause, and your clinician can put it in context.

Common causes

  • Blood drawn within hours of an allergic reaction, when tryptase is expected to be high
  • An inherited trait called hereditary alpha-tryptasemia (extra copies of a tryptase gene), found in up to about 6 in 100 people and often causing no problems
  • Reduced kidney function
  • Older age
  • Higher body weight (obesity)
  • Mast cell conditions, such as systemic mastocytosis, in which the body has too many mast cells. These are much less common
  • Some blood disorders, parasite infections and rare inherited conditions
  • Rarely, antibodies in the blood that confuse the test and give a falsely high result

What can help

  • Ask your clinician whether the blood was drawn at the right time after your reaction, and whether a baseline sample at least 24 hours later is needed
  • Ask whether a genetic test for extra tryptase gene copies (TPSAB1) would help explain a baseline level that stays high
  • Ask whether your kidney function, weight or other health factors could explain the level
  • If you have had reactions to insect stings, foods or medicines, ask whether seeing an allergist makes sense

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: up to 11.4 µg/L. Source: Allergologie Select, Diagnostics (Basel), World Allergy Organization Journal, ARUP Laboratories, Mayo Clinic Laboratories, University of Washington Department of Laboratory Medicine and Pathology, Labcorp.

What can affect your result

  • When the blood was drawn: after a reaction, levels peak about 1 to 2 hours after symptoms start, and a baseline sample is taken at least 24 hours after the reaction is over
  • Inherited extra copies of the alpha-tryptase gene (hereditary alpha-tryptasemia), which raise the baseline level
  • Kidney function, age and body weight: baseline levels are higher with reduced kidney function, older age and obesity
  • Type of reaction: food-triggered reactions often raise tryptase little or not at all
  • Smoking and alcohol: smoking has been linked to higher baseline levels and alcohol to lower ones
  • The lab and test, because upper limits differ between labs (for example 10.9 to 13.2 µg/L)
  • Timing matters: after anaphylaxis, tryptase rises from about 15 minutes to 3 hours after symptoms start and peaks at about 1 to 2 hours, so a sample drawn too early or too late can miss the rise (WAO 2020).
  • A level in the usual range does not rule out an allergic reaction. About 36 to 40% of peak levels after anaphylaxis stayed under 11.4 µg/L in one guideline, and food-triggered reactions often raise tryptase little or not at all.
  • An inherited extra copy of the alpha-tryptase gene, reduced kidney function, older age and obesity can raise the baseline level without a mast cell condition.
  • Rarely, interfering antibodies in the blood (heterophilic antibodies) can give a falsely high result.

After a reaction, ideally 30 to 120 minutes after symptoms start and no later than about 4 hours. A baseline sample is taken at least 24 hours after the reaction is over. After a reaction, tryptase rises within hours and a sample is best taken 30 to 120 minutes after symptoms start. A baseline level is meant to be taken at least 24 hours after the reaction is over.

When to talk to a clinician

Call 911 or your local emergency number right away for signs of a severe allergic reaction: trouble breathing, swelling of the face, lips or throat, dizziness or fainting, repeated vomiting, or widespread hives. If you have had a reaction and tryptase was not measured within a few hours, ask your clinician whether a baseline level and an allergist visit make sense. A baseline level above your lab's range is worth discussing with your clinician, and a baseline above about 20 µg/L is one reason clinicians look more closely for mast cell conditions.

Questions you could ask

  • How does my tryptase level fit with my sting or allergy test results?
  • Should I see an allergist about my reactions?
  • Was my blood drawn at the right time after my reaction?
  • Would a baseline sample at least 24 hours later help?
  • Could my kidney function, age or weight explain my level?
  • Would a test for extra tryptase gene copies (TPSAB1) help explain it?

Questions people ask

Why do some people get two tryptase tests?

A level taken within a few hours of a reaction shows whether mast cells released their contents. A level taken at least 24 hours after you have recovered shows your usual level. Clinicians compare the two. One widely used rule looks for a rise of at least 20% plus 2 µg/L over your baseline.

My baseline tryptase is a bit above the range. Does that mean I have a mast cell disease?

Not usually on its own. An inherited trait that affects up to about 6 in 100 people is the most common reason for a high baseline, and kidney function, age and weight can also raise it. One 2023 review says an increase up to 15 µg/L without symptoms is no reason for further testing. Your clinician decides what fits you.

Can my tryptase be in the usual range after a severe allergic reaction?

Yes. In one international guideline, about 36 to 40% of peak levels after anaphylaxis stayed under 11.4 µg/L, and food-triggered reactions often raise tryptase only a little or not at all. A result in the usual range does not rule out an allergic reaction.

Show the science and sources

Units

  • 1 µg/L = 1 µg/L
  • 1 µg/L = 1 ng/mL

For clinicians and researchers

Total serum tryptase, measured by a fluorescent enzyme immunoassay (ARUP lists a quantitative fluorescent enzyme immunoassay and notes that it does not distinguish alpha from beta tryptase; the widely used ImmunoCAP assay measures all isoforms in monomeric and tetrameric form). Resting mast cells constitutively secrete monomeric pro-tryptase, which reflects mast cell burden; degranulation releases mature tetrameric tryptase, so total tryptase rises in acute activation (WAO 2020; Beyens 2023). Upper reference limits differ: the manufacturer's 95th percentile is 11.4 µg/L (DGAKI 2023), ARUP prints 10.9 µg/L or lower, Mayo Clinic Laboratories prints under 11.5 ng/mL, the University of Washington lab prints 0 to 12 ng/mL, Labcorp prints 2.2 to 13.2 µg/L, and ECNM and AIM experts propose 1 to 15 µg/L for a normal baseline. Paired sampling is the key use: an acute sample, ideally 30 to 120 minutes after symptoms start and up to about 4 hours, and a baseline at least 24 hours after the event. The consensus formula calls mast cell activation when the acute value is at least 1.2 times baseline plus 2 µg/L (the 20% + 2 rule; WAO 2020, Beyens 2023). It misses some reactions; in the WAO guidance 36 to 40% of peak levels remained under 11.4 µg/L, and food-triggered anaphylaxis often shows a small or no rise. A baseline above 20 µg/L is a minor World Health Organization criterion for systemic mastocytosis, but mastocytosis cannot be excluded at lower values, the criterion does not apply when another blood neoplasm is present, and it should be adjusted in hereditary alpha-tryptasemia (DGAKI 2023, Beyens 2023). Hereditary alpha-tryptasemia is an autosomal dominant increase in alpha-coding TPSAB1 copy number, found in up to 6% of the general population and the most common cause of an elevated baseline in the review cited (about 91%, ahead of chronic kidney disease at 7%); a baseline above 8 µg/L in someone with anaphylaxis or recurrent mediator-related symptoms is a reason to consider TPSAB1 genotyping, and an increase up to 15 µg/L without symptoms is described as no reason for further evaluation (Beyens 2023). Other causes of a raised baseline include chronic kidney disease (probably through stem cell factor, since tryptase is not cleared by the kidneys), obesity, age, helminth infection, hematologic neoplasms and rare genetic conditions such as GATA2 variants; heterophilic antibody interference can cause false positives. Elevated baseline tryptase is the greatest risk factor for severe insect sting reactions, and the associated risk begins below the 95th percentile (DGAKI 2023). Tryptase is reasonably stable in stored serum (Beyens 2023).

LOINC 21582-2 (primary). Specimen: serum-or-plasma.

Sources

  1. Tryptase (ARUP test 0099173), ARUP Laboratories
  2. Diagnosis and treatment of Hymenoptera venom allergy: S2k Guideline of the German Society of Allergology and Clinical Immunology (DGAKI), Allergologie Select (2023)
  3. Diagnostic Significance of Tryptase for Suspected Mast Cell Disorders, Diagnostics (Basel) (2023)
  4. World Allergy Organization Anaphylaxis Guidance 2020, World Allergy Organization Journal (2020)
  5. Tryptase, Serum (test ID TRYPT), Mayo Clinic Laboratories
  6. Tryptase Result (UW Medicine Laboratory Test Guide, test TRYPR), University of Washington Department of Laboratory Medicine and Pathology
  7. Tryptase (test 004280), Labcorp

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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