ABSTRACT
Aim: The aim of our study was to do an agreement analysis of two different laboratory
methods used to measure electrolytes i.e., between the ISE based Beckman Coulter Synchron
CX9 PRO Biochemistry analyzer and RAL′s Ion3 Flame Photometer (Técnica para el Laboratorio,
Barcelona, Spain), in serum samples.
Materials and Methods: This cross sectional study was done over a period of three months from September′09
through December′09 on routine biochemistry samples. A total of 6492 samples were
received for routine biochemistry analysis from those 630 blood samples were randomly
processed for this study. Two ml of sample was taken in a plain gel tube (LABTECH
Disposables, Ahmedabad, India), centrifuged and further processed using both systems
within one hour of the sampling to obtain the Na and K concentrations in the samples.
The bias and variability of differences in measured values were analyzed according
to Bland and Altman method.
Results: Flame photometry method has drawbacks such as low throughput, requires manual operation,
is a time consuming procedure. Ion selective electrodes technique is a more universal
method for the high throughput determination of electrolytes in physiological samples;
Beckman Coulter Synchron CX9 PRO is an example of such a system. The mean difference
between the two methods (standard minus test) and 95% limits of agreement for sodium
in serum was -7.8±17.3 (-42.2 to 26.6) and in urine was -22±41 (-104 to 60). 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). With
95% confidence interval, the value of sodium and potassium as determined by both the
methods lie between the upper and lower limit showing 95% limits of agreement.
Conclusion: Good degree of agreement was seen on comparing the two methods for measuring the
electrolytes; the use of Synchron CX9 in place of Flame photometer for electrolyte
analysis in serum and urine is justified or use the two interchangeably.
Keywords
Electrolyte measurement - flame photometry - ion selective electrodes method
