Comparative evaluation of the radioenzymatic method for the determination of urinary histamine with a mass spectrometric assay.

Considerable inaccuracy and unreliability have recently been demonstrated to be associated with the widely used radioenzymatic methods for the determination of histamine in biological fluids. Urine appears to inhibit the methylation of histamine by histamine N-methyltransferase such that the radioenzymatic assay underestimates the concentration of histamine present in urine. Directly comparing the radioenzymatic assay with a recently developed reference method using mass spectrometry for the determination of urinary histamine, up to 34-fold differences in the levels of urinary histamine were found with the two methods.