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Tryptase is a neutral protease located in the secretory granules of mast cells that is released into the circulation during mast cell activation and degranulation. Measurement of serum tryptase concentration is useful in assessing mast cell activation, which may occur as a result of anaphylaxis, allergen challenge, or systemic mastocytosis. Serum tryptase levels peak in 1 to 2 hours and may return to normal in 3 to 4 hours, but may remain elevated for up to 48 hours. Tryptase concentrations above 11.5 ng/mL indicate mast cell activation.

False negative results may be obtained if the specimen is drawn more than 12 hours after an anaphylactic episode. Tryptase is a better marker of mast cell activation than histamine, because the latter is cleared from blood within minutes.

Reference value is 0 to 11.5 ng/mL.

Specimen requirement is one SST tube of blood. The tube should be refrigerated after collection.

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