How to diagnose mast cell activation syndrome: practical considerations.

Mast cells (MCs) are an important component of the immune system. Their physiological function is involved in multiple areas of human physiology, thus symptoms of their increased activation vary greatly from severe allergic reactions, such as anaphylaxis, to chronic symptoms, such as depression or osteoporosis. Studies on mastocytosis revealed a subgroup of patients presenting symptoms of increased MC degranulation, defined as mast cell activation syndrome (MCAS). This population includes patients with primary MCAS with clonal abnormal MCs, who do not fulfill the criteria for mastocytosis. These symptoms often overlap with comorbidities, which makes the diagnosis and treatment of MCAS difficult. The syndrome is diagnosed on the basis of 3 criteria: 1) the presence of typical symptoms; 2) elevation of serum tryptase levels; and 3) response to anti-mediator treatment. The diagnosis of MCAS is important especially in patients with anaphylaxis or osteoporosis who require the use of an epinephrine emergency kit and insect venom immunotherapy. In this review, genetic mechanisms and typical symptoms of MCAS as well as its diagnostic criteria and implications were discussed, with a special emphasis on practical guidance with the aim to improve patient care.