Evaluation of an Automated Selective-Ion Electrolyte Analyzer for Measuring Na+, K+, and Cl- in Serum

Abstract

Abstract An automated analyzer, in which ion-selective electrodes are used to measure sodium, potassium, and chloride in serum, was assessed in a clinical setting. Day-to-day precision, evaluated by replicate analysis of serum pools, yielded the following coefficients of variation for sodium, potassium, and chloride, respectively: 0.99%, 1.39%, and 0.67%. Values for chloride in both commercial control sera and aqueous standards were linearly related to concentration over a range of at least 10-220 mmol/liter; however, results with the potassium and sodium electrodes showed slight curvilinearity over the range 0-24 and 10-220 mmol/liter, respectively. Mean recoveries for sodium, potassium, and chloride for concentrations covering the clinically important ranges were 98.3-102.3%, 95.9-100.0%, and 97.8-102.0%. The only important differences between experimental and comparison methods in sera were falsely high values obtained with the ion-selective electrode for K+ (caused by supranormal ammonia concentrations) and for Cl- (caused by administered bromide). Mean sodium and chloride values obtained with the electrode did not differ significantly from values obtained by flame-emission photometry or coulometry for duplicate patients’ specimens, but potassium values did differ slightly (P = .05).