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Tryptase (mast cell tryptase) serum

Category Immunology
Test background

Measurement of serum mast cell tryptase level is used to confirm a mast cell degranulation event and is the only reliable laboratory marker of anaphylaxis. A mast cell tryptase level >20µg/L is one of the diagnostic criteria for mastocytosis.

The half-life of serum tryptase is 2-3 hours and so the timing of sample draw for tryptase testing is crucial, too early and there is a risk of falsely normal levels, too late and tryptase levels may have fallen back to within the normal range. UK NICE (CG134) recommend two tryptase samples be taken in the acute setting, immediately and within 1-2hours but no longer than 4 hours of the beginning of clinical symptoms, followed by a baseline tryptase sample taken over 24 hours after symptoms have resolved.

Anaphylaxis is not excluded if tryptase levels are within the normal range. A mast cell activation event can be demonstrated if acute tryptase level is equal to or greater than 1.2 x baseline tryptase + 2µg/l.

Causes of raised baseline serum tryptase levels include hereditary alpha tryptasemia (HAT), mastocytosis, helminth infection, metabolic syndromes and chronic renal failure.

Clinical Indications

Investigation of anaphylaxis and mastocytosis

Reference range

<14.0 µg/l
Reference range currently under review

Sample & container required Serum (RST rust top)
Sample volume 5mL blood (1 mL serum)
Turnaround time 4 Days