Measurement of urinary N tau-methylhistamine excretion: correlation of a newly developed radioimmunoassay (RIA) with gas chromatography mass spectrometry (GCMS).

A newly developed radioimmunoassay (RIA, Y) for the determination of urinary N tau-methylhistamine concentrations was correlated with gas chromatography mass spectrometry (GCMS, X). In 34 urine samples, with histamine and N tau-methylhistamine levels within our reference values, the correlation was: Y = 1.47X -0.245 mumol/l (r = 0.92; p-slope less than or equal to 0.0001). In 14 pathological urine samples, derived from patients with mastocytosis and having upper reference values, the correlation was: Y = 1.75X - 1.02 mumol/l (r = 0.93; p-slope less than or equal to 0.001). In spite of the greater specificity of the monoclonal antibody for N tau-methylhistamine compared with that of histamine, relatively high urinary histamine concentrations gave a false positive influence on the RIA results, which was 100% when the histamine/N tau-methylhistamine ratio was about 19. Clear cases of mastocytosis can be diagnosed, using the RIA-kit, but for a more precise N tau-methylhistamine value GCMS analyses will remain necessary.