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.

Glucose variation in centrifuged serum and lithium-heparin gel tubes stored for up to 96 hours at room temperature or 4 °C.

This study aimed to verify glucose stability within centrifuged serum and lithium-heparin tubes stored at room temperature (RT) or 4 °C. Sixty paired serum (plus gel separator), lithium-heparin (plus gel separator) and K2-EDTA tubes were centrifuged within 30 min from collection. Thirty serum and lithium-heparin tubes were then stored at RT, whilst the other 30 serum and lithium-heparin tubes were kept at 4 °C. Complete cell blood count was performed in serum and plasma after centrifugation, as well as in K2-EDTA paired whole blood tubes. Glucose was measured immediately after centrifugation and 3, 6, 24, 48, 72 and 96 h afterwards. Immeasurable blood cells values were found in serum, whilst residual leukocytes and platelets were present in lithium-heparin plasma. Regardless of storage conditions, glucose concentration decreased 3 h after centrifugation in lithium-heparin tubes, displaying uninterrupted reduction until 96 h. Mean decrease per hour was higher in plasma tubes stored at RT than at 4 °C. Performance specification was exceeded between 6 and 24 h of storage in most plasma tubes. Glucose concentration significantly decreased in serum tubes between 24 and 48 h, regardless of storage conditions. The mean glucose variation never exceeded performance specification throughout the study period. Mean glucose decrease per hour in plasma was not associated with blood cells counts before and after centrifugation, and was probably attributable to the presence of blood cells entrapped within the gel. Delayed glucose measurement in centrifuged serum tubes may be clinically viable up to 96 h, whilst it may be unadvisable in centrifuged lithium-heparin tubes.