Retesting Intervals for Tryptase
Authors: CADTH  
Published: September 2024

What Is the Issue?

Tryptase is a serine protease primarily produced and released by mast cells. Tryptase measures are most used to diagnose and manage anaphylaxis and mastocytosis, and the timing of tryptase measurement is crucial for its utility.
The clinical utility of tryptase remains unclear, and available evidence showed that more than 30% of patients with acute anaphylaxis did not exhibit an elevated tryptase level, which suggests that repeated tryptase testing may be overused in this population.
Appropriate retesting intervals or frequency for tryptase retesting in patients with anaphylaxis or mastocytosis remain unclear.

What Did We Do?

To inform decisions about the use and timing of repeat tryptase testing for patients with confirmed or suspected anaphylaxis and patients with cutaneous or systemic mastocytosis, we identified and summarized related recommendations and publications on the potential biological or physiological factors that may impact retesting intervals in these populations.
We searched key resources, including journal citation databases, and conducted a focused internet search for relevant evidence published since 2014. One reviewer screened articles for inclusion based on predefined criteria, critically appraised the included evidence-based guidelines, and narratively summarized the findings.

What Did We Find?

For patients with suspected anaphylaxis, identified guidelines suggest measuring tryptase levels 1 to 2 times during the event onset (e.g., immediately or within 4 hours) and 1 to 2 times after resolution of symptoms (e.g., after 24 hours) to establish baseline tryptase levels. These recommendations were based on very low certainty of evidence.
For patients with systemic mastocytosis, 1 evidence-based guideline in Brazil recommends testing tryptase once a year, which is based on very low certainty of evidence.
Baseline tryptase level varies very little over time within the same individual and is determined by their genetic background.
For patients with anaphylaxis, the timing of the peak tryptase level is from 1 minute to 6 hours (median 30 minutes), and the half-life of serum tryptase is about 1.5 hours to 2.5 hours and needs up to 24 hours to return to baseline level.
We did not find any recommendations that met our inclusion criteria regarding the minimum retesting interval for tryptase testing or the use of repeat or serial tryptase testing in patients with confirmed or suspected anaphylaxis or with cutaneous or systemic mastocytosis.

What Does It Mean?

The available recommendations suggest testing blood tryptase at the acute (1 or 2 times) and baseline phases (1 or 2 times) for patients with suspected anaphylaxis. There is little rationale for the ongoing monitoring of tryptase levels beyond the recommended 4 time points for patients with anaphylaxis.
For patients with mastocytosis, the guidelines recommend retesting tryptase only once a year and do not support frequent repeat tryptase testing within a year.
Decision-makers and clinicians should consider the cost of tryptase testing, potential burden on health care resources, local lab capacity, or accessibility of testing facilities when making decisions regarding tryptase retesting.
Given the very low-quality evidence regarding measuring tryptase and the unclear utility of tryptase testing for patients with anaphylaxis, future research that focuses on the clinical utility of tryptase relative to clinical assessment for anaphylaxis is needed.