Reliability of Venous Electrolyte Measurement from the Point-of-Care Blood Gas AnalyserA Comparative Study with the Central Laboratory Autoanalyser in a Tertiary Care Emergency Department

Abstract

Introduction: Emergency Departments (EDs) utilise Point-OfCare (POC) equipment based on which the physicians decide on resuscitation and management. Along with many other parameters, POC Blood Gas Analysers (BGA) in the ED provide quick results on blood electrolytes, enabling physicians manage dyselectrolytemia immediately compared to the prolonged turnaround time from Central Laboratory (CL) Auto Analysers (AAs). ED physicians usually wait for AA result for confirmation of dyselectrolytemia. Aim: To compare sodium and potassium ions measurement in venous sample pairs between BGA and AA, and whether results from BGA could be acceptable as per standard norms, thus avoiding time delay in management of dyselectrolytemia and saving cost. Materials and Methods: This prospective observational study was done in the ED of a tertiary care centre in North Kerala. After Institutional Ethics Committee approval and obtaining informed consent, the study was conducted in 224 adult patients during July 2018 to July 2019 with clinical indications for Venous Blood Gas (VBG) and serum electrolytes as part of management. Venous samples from the patients were collected successively in heparin rinsed syringes and plain bottles and analysed in the POC BGA (ABL800 Flex Radiometer) in the ED and AA in the hospital central laboratory (Beckman Coulter AU 5800), respectively. Mean, standard deviation and two-tailed p-value were used for statistical analysis. Bland-Altman plots, box plot and scatter diagram were used for inter instrument comparison of results. Results: Out of 224 (122 males and 102 females) paired venous samples, the mean sodium (Na) were 131.6± 9.0 mmol/L (BGA) and 131.7±8.3 mmol/L (AA) with mean difference of 0.1 mmol/L. The mean patassium (K) was 3.6±0.7 mmol/L (BGA) and 4.0±0.77 mmol/L (AA) with mean difference of 0.4 mmol/L. The 95% limits of agreement for Na and K between equipment were -6.13 to 5.95 mmol/L and -1.28 to 0.6 mmol/L, respectively. Karl Pearson Correlation of Na and K assessment were 0.94 and 0.77 (p <0.01), respectively. These values were within the accepted limit of the United States Clinical Laboratory Improvement Amendments (difference of 4 mmol/L in sodium measurements and 0.5 mmol/L in potassium measurement from the gold standard). No Indian Clinical Laboratory Improvement Amendments were found. Conclusion: The authors found no statistically significant difference between BGA and AA in sodium and potassium measurement. This will enable emergency physician to make critical decisions by trusting sodium and potassium values obtained from the POC BGA.

Keywords

• dyselectrolytemia
• potassium
• sodium