Defining Acid-Base Status in Hemodialysis: Is Bicarbonate Enough?

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

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.