Comparison of four electrolyte instruments using the proposed NCCLS protocol for evaluation of precision and accuracy of automated instruments.

We compared four instruments, [Sequential Multiple Analyzer Computer (SMAC), AutoAnalyzer II (AAII), StatLyte and PVA-4] for the determination of Na, K, Cl and CO2 using the National Committee for Clinical Laboratory Standard's (NCCLS) protocol (PSEP-1) for evaluation of precision and accuracy of automated instruments. The protocol was applied concurrently to all four instruments. The repeatability results showed SMAC to have the highest precision among-days for K, Cl, and CO2 whereas StatLyte showed the highest precision among-days for Na. The PVA-4 had the best within-run precision for Na and Cl while the AAII and SMAC had the best within-run precision for K and CO2 respectively. Systematic biases among the instruments were small for Na and K. The AAII exhibited a nearly constant bias at all concentrations of Cl relative to the other three instruments. For CO2 the SMAC showed a large proportional bias compared with the other three instruments.