Mast Cell Tryptase

Mast cell tryptase is a proteolytic enzyme predominantly found in mast cells. Measuring its levels in the blood can be clinically useful in several contexts:

  1. Anaphylaxis:
    1. Diagnosis: A significant increase in serum tryptase levels compared to a patient’s baseline can help confirm a diagnosis of anaphylaxis. Tryptase levels usually peak 1-2 hours after the onset of an anaphylactic episode and can remain elevated for several hours.
    2. Severity: Higher levels of tryptase can correlate with more severe anaphylactic reactions.
  2. Mastocytosis:
    1. Diagnosis and Monitoring: Mastocytosis is a group of disorders characterized by an abnormal accumulation of mast cells in one or more organ systems. Elevated levels of tryptase can support a diagnosis of systemic mastocytosis, especially when other clinical criteria are met. Moreover, serial measurements can be used to monitor the course of the disease or the effectiveness of therapy.
    2. Prognosis: In patients with systemic mastocytosis, persistently elevated tryptase levels or increasing levels over time can indicate a worse prognosis.
  3. Mast Cell Activation Syndrome (MCAS):
    1. Supporting Diagnosis: MCAS is characterized by episodic symptoms consistent with mast cell mediator release affecting two or more organ systems. While the diagnosis is complex and involves various criteria, an elevation in tryptase levels during an episode (compared to the patient’s baseline) can support the diagnosis.
  4. Other Conditions:
    1. Certain hematological disorders: Elevated tryptase levels can sometimes be seen in conditions like myelodysplastic syndrome or chronic myelomonocytic leukemia.
    2. Advanced systemic mastocytosis with associated hematologic neoplasm: In this condition, the tryptase level can help in diagnosis and prognostication.

It’s important to interpret serum tryptase levels in the context of the clinical presentation and other diagnostic tests. Additionally, while an elevated tryptase can support the diagnosis of conditions like anaphylaxis or mastocytosis, normal levels do not necessarily rule them out, especially if the sample is taken > 6 hours after the onset of symptoms.