Role of the fractional excretion of uric acid in the study of hyponatremia
Abstract
Introduction: Hyponatremia is the most common hydroelectrolitic disorder in hospitalized patients. It is essential to acquire an early understanding of the extracellular liquid (ECL) status for the study of the causes of hyponatremia and its subsequent treatment. The possibility of using the fractional excretion of uric acid (FEUA) as a supplementary tool to distinguish normal ECL from reduced ECL has been considered, including patients undergoing diuretic treatment. Methods: The typical clinical and laboratory parameters were examined at the time of the diagnosis of hyponatremia in 45 patients prospectively selected, to define the status of ECL. Once defined, the FEUA was estimated. Results: For the 21 patients within the reduced ECL group, blood pressure, natriuria, fractional excretion of sodium, fractional excretion of urea and FEUA were significantly lower (p < 0.05) than for the 24 patients within the normal ECL group. Among these variables, the FEUA was the one which showed more sensitivity and specificity to predict a reduced ECL, with a cutoff value < 10.9 %. Within the of 15 patients on diuretic treatment, FEUA < 10.9 % had a 100% sensitivity and a 100% specificity to predict a reduced ECL. Conclusion: Therefore, the FEUA should be included in the study protocol of a patient with hyponatremia, since when performed in an isolated sample of blood and urine, it constitutes a simple and efficient method to be implemented under emergency situations, especially in patients receiving diuretics.
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