Improved diagnosis of mastocytosis by measurement of urinary histamine metabolites.

In an attempt to facilitate the diagnosis of mastocytosis, we measured the urinary excretion of histamine and two of its main metabolites (N tau-methylhistamine and N tau-methylimidazoleacetic acid) in eight adults with this disorder. All patients had above-normal values for the metabolites of histamine, whereas only three had above-normal values for histamine. In both 24-hour and randomly voided urine specimens, the determination of histamine metabolites is more specific and sensitive for the diagnosis of mastocytosis than the determination of histamine itself.