Tryptase

Why this test?

For differential diagnosis of diseases accompanied by symptoms of mast cell activation (anaphylactic reactions, systemic mastocytosis); 

To control the treatment of mastocytosis with immunosuppressive drugs.

In what cases is it prescribed?

In the presence of symptoms of mast cell activation: itching, urticaria, rhinorrhea, sneezing, coughing, shortness of breath, chest pain, lacrimation, hypotension, abdominal pain, heart rhythm disturbances, loss of consciousness, and others; in the presence of pigmented urticaria; in the treatment of mastocytosis with immunosuppressive drugs.

Test information

Tryptase is a trypsin-like enzyme found in the granules of mast cells (fat cells) and basophils. The concentration of tryptase in mast cells is approximately 300 times higher than in basophils. There are 5 isoforms of this enzyme (alpha, beta, gamma, delta and epsilon), and beta-tryptase is the predominant isoform in mast cell granules. The physiological role of tryptase is not completely clear, but its various pro-inflammatory effects are known, including inactivation of bronchodilator mediators, destruction of vasoactive intestinal peptide, increased permeability of the vascular wall and expression of VCAM-1 adhesion molecules. As a result of activation and degranulation of mast cells, the level of tryptase in the blood increases.

Activation of mast cells is accompanied by characteristic allergic symptoms in the form of itching, urticaria, rhinorrhea, sneezing, coughing and lacrimation, and can sometimes reach the degree of anaphylaxis. These signs, however, do not always indicate an allergy, they can also be observed in systemic mastocytosis of other myeloproliferative diseases, which are characterized by the activation of mast cells and an increase in the level of tryptase in the blood even without any allergen. For differential diagnosis of diseases with symptoms of mast cell activation, laboratory tests are carried out, including blood tryptase analysis.

There is no consensus on what level of increase in tryptase is considered pathological. It is believed that an excess of tryptase concentration of more than 20 ng / ml from the normal value (less than 10-15 ng / ml) or at least 20% of the increased value (more than 15 ng / ml) indicates the activation of mast cells.

It is recommended to examine the level of tryptase several times: against the background of clinical symptoms of the disease, after a few hours and after a few days after the cessation of symptoms. The half-life of tryptase is longer than, for example, histamine, which makes tryptase a very convenient clinical and laboratory marker of mast cell activation. Patients with elevated baseline tryptase should be screened for mastocytosis. A persistent increase in the level of tryptase more than 20 ng / ml is one of the small criteria for the diagnosis of mastocytosis. The concentration of tryptase usually reaches high values (more than 200 ng / ml) with an aggressive course of systemic mastocytosis. Against the background of the use of immunosuppressive drugs, the concentration of tryptase decreases, so this clinical and laboratory marker can be used to control the treatment of mastocytosis. It should be noted that persistent increase of tryptase is a characteristic, but not absolutely specific sign of mastocytosis (specificity - about 98%). It can be observed in other myeloproliferative diseases, chronic renal failure and even in healthy people. Also, the sensitivity of the tryptase test for mastocytosis is about 83%, so a negative result does not rule out the disease.

Normalization of the tryptase level 12-14 hours after the cessation of symptoms, on the contrary, indicates an allergic episode. Interestingly, in some patients with obvious symptoms of anaphylaxis, the level of tryptase remains within the normal range. This may be partially due to the effect of tryptase (with a local increase in its concentration, for example, with swelling of the larynx, which is not accompanied by an increase in the level of tryptase in the blood) or the predominant participation of basophils, and not mast cells, in the pathogenesis of an anaphylactic reaction in this patient. Thus, just as in the case of mastocytosis, a negative test result does not rule out anaphylaxis.

The study of tryptase can be supplemented by the study of other mediators of mast cells (histamine, leukotrienes and prostaglandins), as well as general and specific IgE immunoglobulins. If an allergy is suspected, it is advisable to conduct allergy skin tests 4-6 weeks after the episode of the disease.