ENZYMATIC DETERMINATION OF SODIUM, POTASSIUM, AND CHLORIDE IN ABNORMAL (HEMOLYZED, ICTERIC, LIPEMIC, PARAPROTEINEMIC, OR UREMIC) SERUM SAMPLES COMPARED WITH INDIRECT DETERMINATION WITH ION-SELECTIVE ELECTRODES

We evaluated the effect of hemolysis, icteric discoloration, lipemia, paraproteinemia, and uremia on enzymatic methods for determining sodiu m, potassium, and chloride, according to the National Committee for Cl inical Laboratory Standards EP7-P proposals for testing interference f rom endogenous substances. The sodium, potassium, and chloride assays (reagent kits supplied by Boehringer Mannheim) were based on electroly te-dependent beta-galactosidase, pyruvate kinase, and alpha-amylase, r espectively. The results were compared with those obtained by indirect ion-selective electrodes (ISE), which in turn had been validated by f lame photometry. We analyzed the samples with Hitachi 717, 737, and 91 1 chemistry analyzers and with an IL943 flame photometer. The enzymati c results were in good agreement with those by ISE, the interference-r elated differences generally being without clinical significance; howe ver, none of the enzymatic methods could analyze grossly lipemic sampl es.