Validation of a simple formula for calculation of serum chloride with estimated value using ion selective electrode

Introduction and Aim: The maintenance of fluid balance in the intracellular and extracellular compartmentsis by two major electrolytes, namelysodium and chloride. An increase in sodium is associated with an increase in chloride level and vice versa. The normal reference ranges of sodium and chloride in blood differ by 40mmol/L.On this basis, chloride values can be calculated manually by subtracting 40 from the estimated sodium value. Methods: The study population included 150 normal subjects and 150 diabetic patients.Sodium and chloride, as estimated by the ISE method, were noted in75 random and fasting samples of diabetic group and non-diabetic group. Chloride values were calculated by the new formula(Serumchloride=Serumsodium-40). Mean values of chloride obtained by estimation and calculation were then compared in both diabetics and normal controls. Correlation analysis of estimated chloride and calculated chloride was done by Pearson’s correlation. Results: Chloride determined by the ISE method showed a statistically significant positive correlation with calculated value both in normal and diabetic groups. Further,estimated chloride and calculated chloride values were comparable within the groups in controls and diabetics irrespective of the type of sample collected, ther > 0.95, p=0.0001 in fasting samples of both groups and r = 0.899, p=0.0001 in random samples of both groups. The percentage error calculated between fasting and random samples of both the groups was negligible (less than 1%),clearly indicating the accuracy and reliability of the value obtained by using the new simple formula for chloride estimation. Conclusion: On the availability of estimated sodium, chloride values can be calculated by subtracting forty from the same. The values so obtained are reliable in normal as well as the diabetic state where dysnatremia is common.