Tryptase

Tryptase is often ordered as part of the diagnostic assessment of a patient suspected of having mastocytosis (either cutaneous or systemic).^3-5 Serum levels are thought to correlate with mast cell "burden" in these patients.⁵ Mastocytosis is considered in the differential diagnosis of patients that experience severe allergic reactions without any identifiable specific trigger. Systemic mastocytosis can produce symptoms suggestive of organ involvement, such as peptic ulcers, chronic diarrhea, and joint pain. These patients may display evidence of enlargement of the liver, spleen, or lymph nodes. There may be skin involvement with rashes or characteristic red blistering lesions.

Tryptase may be ordered to help confirm anaphylaxis as the cause of an individual's acute symptoms, especially when the diagnosis is not clear and/or the symptoms are recurrent.^6,7 With anaphylaxis, tryptase levels typically peak about one to two hours after symptoms begin and then decline slowly within the next three to six hours. The biological half-life for tryptase is about two hours.

Systemic mastocytosis is a risk factor for anaphylactic reactions, particularly in response to drugs^8,9 and insect stings.^10-15 Patients with elevated baseline tryptase levels may be at increased risk for severe anaphylactic reactions. The risk associated with baseline elevated tryptase levels is greater in individuals with a known history of severe systemic reactions. Transiently increased tryptase levels measured during severe reaction to an allergen, such as insect venom or an anesthetic drug, suggest that mast cell activation may have had a role in causing the reaction.

Pathological increased levels of tryptase reflect the mast cell burden in certain hematological abnormalities and neoplasms, irrespective if systemic mastocytosis is established or not.¹⁶ Hematological disorders that involve uncontrolled growth of immature myeloid cells in the bone marrow and/or the circulation can produce increased serum tryptase levels. Several therapeutic drugs have been developed for cytoreductive therapy of systemic mastocytosis and hematological neoplasms.¹⁷ During treatment tryptase measurements is a useful monitoring and prognostic tool.