AGREEMENT BETWEEN TWO DIFFERENT FIELD METHODS USED TO MEASURE SERUM ELECTROLYTES IN CLINICAL LABORATORY
Shalini N. Maksane M.Sc.*, Rupali Parikh M.D. and Lakshmi Vaswani D. P. B.
ABSTRACT
Background: The aim of our study was to do an agreement analysis of two different laboratory methods used to measure electrolytes i.e., between the Direct ISE based ABL-800 Basic and Indirect ISE based COBAS-6000 Biochemistry auto-analyzer. Methods: This observational study was conducted from July 2016 to August 2016 on routine biochemistry indoor and outdoor samples. A total of 155 samples were analyzed for the Na+, K+ and Cl- concentrations in the serum. The bias and variability of differences in measured values were analyzed according to Bland and Altman method and Passing-Bablok regression was conducted. Results: The mean difference between the two methods and 95% limits of agreement for sodium in serum was -4.9±3.2 (-5.38 to -4.36) for potassium -.05±0.1 (-0.08 to -0.03) and for Chloride was -7.8±3.1 (-8.3 to -7.3). Similarly, the mean difference between the two methods for potassium values in serum was found to be -0.25±0.75 (-1.75 to 1.25) and in urine was -5.3±38.9 (-83.1 to 72.5). Significant difference in mean values was observed between two methods for serum all three electrolytes (P < 0.001). Conclusions: Good degree of agreement was seen on comparing the two methods for measuring the potassium but not for serum sodium and chloride levels. Two instruments (COBAS-6000 and ABL-800 Basic) cannot be used interchangeably for serum electrolyte measurement. Clinicians must be aware about differences exist between the two ISE technologies. Further, in border-line clinical situations, care must be taken while interpretation of the electrolyte results and taking clinical decision.
Keywords: Electrolyte measurement, Method comparison, Direct ion selective electrodes method, Indirect ion selective electrodes method.
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