No relationship between histamine release measured as metabolite excretion in the urine, and serum levels of mast cell specific tryptase in mastocytosis

To test the hypothesis that histamine release in mastocytosis patients generally occurs without activation of the mast cells, histamine turnover, measured as histamine metabolite excretion in the urine, was compared with the serum level of mast cell specific tryptase, which is released only during active discharge of mast cell granular contents. Twenty mastocytosis patients with a wide range of histamine turnover rates were investigated. Slightly increased levels of tryptase were found in seven patients with no obvious relationship to histamine metabolite excretion. In contrast, there seemed to be a connection between the tryptase level and the severity of symptoms. These results strengthen the view that histamine in mastocytosis is predominantly released from the mast cells without any accompanying active release process. This does not exclude the possibility that, in some mastocytosis patients, a limited number of mast cells, or a subpopulation, may be actively secreting histamine together with tryptase.