Analytical evaluation of direct bicarbonate measurement with the new gem premier chemstat in hemodialysis patients

Abstract

GEM Premier ChemSTAT is a whole-blood analyzer designed for providing a rapid basic metabolic panel, inclusive of creatinine and blood urea nitrogen, with the unique characteristic of providing measured bicarbonate (HCO3 –) levels. The aim of this work was to evaluate the clinical performance of HCO3 – assessment with this analyser in a real-life hemodialysis setting. Imprecision was calculated at different HCO3 – levels, along with assay comparison with Gem Premier 4000 analysers. GEM Premier ChemSTAT displayed an imprecision and a bias (in comparison to GEM Premier 4000) for HCO3 – of 0.4% and 37.3% at 20.8 mmol/L, 1.2% and 25.6% at 16.4 mmol/L, and 2.1% and 11.6% at 11.5 mmol/L, respectively, using three levels of HCO3 – quality control sample ChemSTAT System Evaluator. At direct comparison with the GEM Premier 4000 in the hemodialysis setting, Bland–Altman analysis of HCO3 – levels evidenced a bias (µ) of −4.9 (95% CI, −5.2 to −4.7) mmol/L. Such difference was attenuated by recalculating the GEM ChemSTAT expected HCO3 – values from pH and pCO2 using the Henderson Hasselbach equation, µ=–0.07 (95%CI, −0.19 to 0.05) mmol/L (p = .24). In conclusion, our results show a remarkable difference between the HCO3 – values reported by GEM ChemSTAT or GEM 4000. New reference values for GEM ChemSTAT HCO3 – shall hence be defined according to our findings. We suggest that further investigation and a re-evaluation of the reference range should be made before extending the clinical use of this device.