Tryptase measures the total level of tryptase released by mast cells into the circulation.
A transient elevation in tryptase can occur after a severe allergic reaction, known as anaphylaxis, with levels returning to normal on serial testing. Persistently elevated tryptase levels may indicate a rare condition known as mastocytosis.
During acute anaphylaxis, serum tryptase levels are increased from 15 min to 3 hours, or even longer after the onset. Although elevated levels support a diagnosis of anaphylaxis, normal levels do not exclude anaphylaxis. It is recommended to repeat tryptase testing at least 24 hours after symptom resolution to ensure the tryptase concentration returns to within the normal range. In rare instances, an elevated baseline tryptase concentration may uncover systemic mastocytosis.
After a suspected anaphylactic reaction, serial blood samples are recommended for the interpretation of results and include:
- An acute sample, collected between 30 minutes and 2 hours after symptom onset (and after the provision of emergency treatment) is optimal
- NB: a significant increase in tryptase in samples collected up to 4 to 6 hours after an event can still be informative, if earlier samples are unavailable
- NB: in some cases of anaphylaxis caused by an injected drug, a sample taken immediately after resuscitation and another sample taken within 2 hours may be useful
- A baseline sample, collected 24 hours after all signs and symptoms have resolved
References:
Cardona, V., et al. World Allergy Organization Anaphylaxis Guidance 2020. World Allergy Organization Journal (2020) 13:100472.
Weiler, C.R., et al. AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management. (2019)
Ewan, P.W., et al. BSACI guidelines for the investigation of suspected anaphylaxis during general anaesthesia. Clinical and Experimental Allergy (2009) 40:15-31.
