If you are currently undergoing testing for systemic mastocytosis (SM), you’ve likely heard of a molecule called tryptase. Levels of tryptase, which can be measured through a blood test, are a key indicator of SM.
Tryptase plays a central role in both the diagnosis and monitoring of mast cell disorders. But what exactly is serum tryptase, and how does it act as a clinical marker of SM?
What is tryptase?
Tryptase is a protein enzyme that is primarily produced by mast cells and stored in small pockets within the cells known as granules. When mast cells are activated, tryptase and other molecules held in the granules (such as histamine) are released into the body, triggering inflammation.
Even when mast cells aren’t active, they continuously secrete protryptases, which are the inactive form of tryptase. This can be thought of as your “baseline” serum tryptase levels. Mast cell activation causes active tryptase to be released into the bloodstream, raising serum tryptase counts above this baseline level.
Read more about SM testing and diagnosis
Why are serum tryptase levels altered in systemic mastocytosis?
Patients with SM produce not only too many mast cells, but also abnormal mast cells. These abnormal cells infiltrate and release chemical mediators into various tissues in the body, causing elevated levels of total tryptase and symptoms of SM.
When experiencing an acute event, serum tryptase levels might increase even more, above your already-elevated baseline level.
Serum tryptase levels as a diagnostic criterion for SM
In general, the normal range for serum tryptase level is less than 11.5 ng/mL. According to the most recent guidelines for diagnosing SM, a minor criterion of the disease is a serum tryptase level greater than 20 ng/mL.
It’s still possible to be diagnosed with SM if your tryptase levels are below 20 ng/mL, though. There are several criteria that can be met in different combinations to confirm an SM diagnosis.
Serum tryptase levels as a measure of treatment efficacy
In many cases, your doctor may choose to periodically measure your serum tryptase levels as you are receiving treatment for SM. This is a quick and easy way to monitor your biological response to therapy.
In fact, researchers often use tryptase as a marker of mast cell burden during clinical trials. Some examples of trials that have utilized tryptase levels as an endpoint include the PATHFINDER trial of avapritinib and the SUMMIT trial of bezuclastinib.
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