Reliability of current techniques for histamine determination in human plasma: the European external quality control...

The increasing importance of measuring histamine in many clinical conditions and the variety of currently used techniques enforced us to organize an external quality control study (ring study) on the reliability of histamine measurements in European laboratories. Three plasma quality control samples in duplicate (lyophilized) with different amounts of histamine (0-5 ng/ml), two different aqueous histamine standard samples and one solvent sample were sent to 10 laboratories for analysis of their histamine content. The following methods were used: gas chromatographic-mass-spectrometric technique (n = 2), single isotope assay (n = 1), fluorometric-fluoroenzymatic assay (n = 3), radioimmunoassay (n = 3), HPLC technique (n = 2). The study was performed and evaluated according to the approved recommendation (1983) of the International Federation of Clinical Chemistry (IFCC). This first report of the study is concentrated on the imprecision and inaccuracy of the different principal methods and laboratories by comparing two unrelated plasma histamine samples of different analyte concentrations (target values and SD: 4.39 +/- 0.51 ng/ml and 0.99 +/- 0.17 ng/ml). This study showed a fairly good agreement between most participants. 7/11 results obtained with 4 different methods were accurate and precise in the plasma range of histamine (Youden plot). Results outside the borderlines turned out to be a problem of the analyst rather than the method itself. It is suggested to define reference values for plasma histamine and to establish reference laboratories and methods according to the IFCC-guidelines.