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  • Author: A. Nigam x
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Our study was aimed to compare two different laboratory methods used to measure serum sodium and serum potassium level i.e. between the indirect Ion Selective Electrode (ISE) based and Enzymatic based method in Beckman Coulter AU-480, USA, in serum samples.

Materials and methods

This was a cross sectional single center study carried out from September’16 to January’17 on 130 serum samples, to compare the result of serum sodium (S. Na+) and serum potassium (S. K+) level by indirect ISE and Enzymatic method in fully automated biochemistry analyzer (Beckman Coulter AU-480, USA).


To validate new enzymatic method bias, CV% and correlation coefficient were measured for S. Na+ and S. K+. The study has drawn a considerable agreement for measurement of S. K+ level between two methods with mean ± SD of difference was 0.14 ± 0.22 (p = 0.2242), CV% 2.7% and r2 value of 0.94, whereas disagreement for measurement of S. Na+ level with mean ± SD of difference was 2.38 ± 2.36 (p < 0.01), CV% 0.5% and r2 value of 0.82. Bias, CV% and correlation coefficient are acceptable for S. K+, whereas nonacceptable for S. Na+ level measurement as per Clinical Laboratory Improvement Amendments (CLIA) guidelines.


There was a good correlation in S. K+ between both methods whereas values were not correlated well with S. Na+ level. So, enzymatic method can be used as an alternative to indirect ISE method for estimation of S. K+ in small laboratories due to its cost effectiveness, but still intense workout is required for estimation of S. Na+.