Measurement of histamine: a quality control study.

This study evaluated the ability of various laboratories to accurately quantitate histamine in samples of plasma and buffered saline that contained known amounts of histamine. Histamine was dissolved in buffered saline and in plasma and these solutions were lyophilized glass ampules. Sealed ampules were sent to laboratories for analysis of their histamine content by one or more of the following methods: (1) the double-isotope dilution enzymatic method, (2) single-isotope enzymatic method, and (3) manual and automated fluorometry. We analyzed the same solutions in our laboratory by the double-isotope dilution enzymatic method over a 6-mo period; we found a coefficient of variation averaging 26% for these samples over that period of time and our values agreed with theoretical values within 12%. Twelve laboratories analyzed histamine by the double-isotope dilution enzymatic assay. The results revealed a marked variation among laboratories both for the determination of histamine in buffer and, more strikingly, for the determination of histamine in plasma. Three laboratories determined histamine by the single-isotope dilution enzymatic method and one reported results rather close to the standard, while the others reported results that were clearly different from the standards. Five laboratories measured histamine by automated fluorometry and three by manual fluorometry; again, there was marked variation among the results. Overall, these findings indicate that measurements of histamine by different laboratories vary greatly. Thus, absolute values for histamine in biologic specimens in the literature must be regarded with caution.