Modified handling of internal catecholamine standards in radioenzymic assays.

A departure from a radioenzymic procedure widely used for plasma catecholamine assay is reported, in which we use "mean net standards" instead of individual internal standards. Interlaboratory/intermethod analyses validated use of the modified principle and demonstrated its preferential use over the conventional principle. Also demonstrated is use of the modified procedure for calculating catecholamine concentrations of several plasma samples collected from an exercising man and an acceleration-stressed swine. Benefits already derived from use of the procedure include: (a) quantification of certain plasma samples that could not be satisfactorily quantified by conventional options, (b) an apparent gain in analytical precision in virtually all other analyses, and (c) costs of analysis reduced by about 25%.