Tryptase is a serine protease enzyme found naturally within the human body. This enzyme breaks down other proteins, playing a significant part in biological functions like inflammation and immune responses. Its presence in the bloodstream acts as a biochemical signal, providing valuable information about activities within the body’s defense system, which helps medical professionals investigate severe reactions and certain chronic conditions.
Where Tryptase is Produced
The primary source of tryptase is a specialized white blood cell known as a mast cell, which acts as a sentinel for the immune system. These cells are found throughout the body, concentrating heavily in tissues that interface with the outside environment, such as the skin, digestive tract lining, and airways. Mast cells store the enzyme within small, membrane-bound sacs called secretory granules, alongside other chemical mediators like histamine.
Even in healthy individuals, a small, measurable amount of tryptase, called baseline tryptase, is present in the blood. This low level is due to the normal secretion of the enzyme by resting mast cells. The alpha-tryptase isoform often contributes to this steady concentration in the circulation.
Tryptase as a Marker of Acute Mast Cell Activation
A sudden increase in the level of tryptase in the bloodstream is a definitive indicator of acute mast cell activation, a process known as degranulation. This rapid release occurs when mast cells are triggered by an allergen or other stimuli, causing the secretory granules to dump their contents into the surrounding tissue and circulation. The massive release of tryptase and other chemicals is characteristic of a severe systemic reaction, most notably anaphylaxis.
The enzyme itself does not initiate the allergic reaction, but its presence confirms that mast cells were involved in the event. Beta-tryptase, the form stored in the granules, is released in large bursts, making its abrupt elevation a highly specific marker for this acute activation. Tryptase levels typically begin to rise rapidly after the onset of symptoms, peaking in the blood approximately one to two hours after the reaction starts.
Once released, the excess tryptase is cleared from the bloodstream quickly, returning toward the patient’s normal baseline level within 12 to 24 hours. The swift appearance and disappearance of the enzyme make it an ideal biochemical indicator for confirming a recent, severe, mast cell-driven event. While its specific role in the symptoms of anaphylaxis is still being studied, it is known to interact with various proteins and receptors, potentially contributing to symptoms like tissue swelling and changes in blood vessel function.
Diagnosing Conditions Using Tryptase Levels
Measuring the total serum tryptase concentration helps clinicians diagnose both acute and chronic mast cell-related conditions. To confirm an acute event like anaphylaxis, doctors often require two samples: an acute sample drawn shortly after the reaction, and a baseline sample collected at least 24 hours later, when the patient is well. The diagnosis of acute mast cell activation is supported if the acute level shows a significant rise above the baseline level, specifically a 20% increase plus 2 nanograms per milliliter (ng/mL) over the baseline value.
If a patient’s tryptase level is persistently elevated, even when they are not experiencing an acute reaction, it can point toward a chronic underlying disorder. A baseline level consistently above the typical upper limit of normal, often cited as 11.4 ng/mL to 15 ng/mL, warrants further investigation. A baseline serum tryptase level greater than 20 ng/mL is one of the minor criteria used to diagnose the rare condition known as Systemic Mastocytosis. Systemic Mastocytosis involves the abnormal accumulation of mast cells in various organs, such as the bone marrow, liver, or spleen.
Another cause of chronically elevated baseline tryptase is Hereditary Alpha Tryptasemia (H \(\alpha\)T), a relatively common genetic trait. Individuals with H \(\alpha\)T have extra copies of the TPSAB1 gene, which instructs cells to produce more alpha-tryptase, resulting in a stable, elevated baseline level. While many people with H \(\alpha\)T are asymptomatic, this genetic predisposition is recognized as a risk factor for more frequent or more severe anaphylactic reactions.