Comparison of serum tryptase and urine N-methylhistamine in patients with suspected mastocytosis

Abstract Background The disease extent of mastocytosis can be assessed by measurement of mediators or their metabolites, secreted from mast cells. In the present study, we compared results of urinary N -methylhistamine measurements with analysis of total tryptase in serum from patients with suspected mastocytosis. Methods Tryptase in serum was determined with the UniCAP tryptase fluor-enzyme-immunoassay, according to the manufacturers' instructions (Pharmacia, Woerden, Netherlands). N -methylhistamine in urine was determined by competitive radioimmunoassay, according to the manufacturers' instructions (Pharmacia). Results A significant correlation between serum tryptase and urine N -methylhistamine was found both for 138 patients aged 14 or older (Spearman Rank r s  = 0.43, p r s  = 0.46, p  = 0.0267). The between-run coefficient of variation of the tryptase assay was half (6.7%) of the one (13%) found with the urinary N -methylhistamine assay. Both for urine N -methylhistamine and serum tryptase, a significant difference was found between corresponding biopsies with an increased number of mast cell aggregates and biopsies without such an increase. The difference between tryptase levels however was stronger (Mann–Whitney: p  = 0.0012) than the difference between N -methylhistamine levels (Mann–Whitney: p  = 0.0140). Conclusion Serum tryptase discriminates better than urinary N -methylhistamine between patients with an increased number of mast cell aggregates and persons without such an increase.