Mast cells, which are granulocytes found in peripheral tissue, play a central role in inflammatory and immediate allergic reactions. b-Tryptase is a neutral serine protease and is the most abundant mediator stored in mast cell granules. The release of b-tryptase from the secretory granules is a characteristic feature of mast cell degranulation. While its biological function has not been fully clarified, mast cell b-tryptase has an important role in inflammation and serves as a marker of mast cell activation. b-Tryptase activates the protease activated receptor type 2. It is involved in airway homeostasis, vascular relaxation and contraction, gastrointestinal smooth muscle activity and intestinal transport, and coagulation. Serum mast cell b-tryptase concentration is increased in
anaphylaxis and in other allergic conditions. It is increased in systemic mastocytosis and other haematological conditions. Serum b-tryptase measurements can be used to distinguish mast cell-dependent reactions from other systemic disturbances such as cardiogenic shock, which can present with similar clinical manifestations. Increased b-tryptase levels are highly suggestive of
an immunologically mediated reaction but may also occur following direct mast cell activation.Patients with increased mast cell b-tryptase levels must be investigated for an allergic cause.However, patients without increased mast cell tryptase levels should be investigated if the clinical picture suggests severe anaphylaxis.

b-Tryptase levels in serum are elevated in most subjects
with systemic anaphylaxis of sufficient severity to cause
hypotension . b-Tryptase is released from mast cells
in parallel with histamine, but diffuses more slowly than
histamine because it is associated with the protease–
proteoglycan complex . b-Tryptase levels peak at 15–
120 min and with a half-life of 1.5–2.5 h,
histamine levels peak at 5 min and decrease to baseline
within 15–30 min. b-Tryptase testing can be performed on
blood samples obtained 1–6 h after the onset of the
reaction, compared with 15 min for histamine. High
tryptase concentrations can be found in serum obtained
from patients up to 3 days after death from suspected

Serum β-tryptase serves as a specific indicator of mast cell activation and of anaphylactic shock that can be detected by radioimmunoassay.

Normal serum levels are < 1 ng/mL. Levels > 1 ng/mL indicate mast cell activation. After insect sting-mediated systemic anaphylaxis, B-tryptase levels peak 30-60 minutes after the sting and then decline with a 1 1/2 of 2 hours. Peak levels are typically > 5 ng/mL in mast cell-dependent systemic anaphylaxis of sufficient severity to cause hypotension. Levels determined more than 3 to 4 hours after the clinical onset of anaphylaxis will be correspondingly lower and could fall within the normal or mildly elevated range in spite of mast cell activation having occurred. In postmortem sera, a peak B-tryptase level > 10 ng/mL is needed before systemic anaphylaxis should be considered in the cause of death. An apparent elevated level of B-tryptase in a baseline sample suggests systemic mastocytosis