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Abstract: FR-PO290

Optimal Cut-Off Level of Urine Sodium in Differentiating Hypovolemic Hyponatremia and SIADH

Session Information

Category: Fluid and Electrolytes

  • 902 Fluid and Electrolytes: Clinical

Authors

  • Son, Raku, St. Luke's international hospital, Tokyo, Japan
  • Nagahama, Masahiko, St. Luke's international hospital, Tokyo, Japan
  • Komatsu, Yasuhiro, Gunma University, Graduate School of Medicine, Maebashi, Gunma, Japan
  • Nakayama, Masaaki, St. Luke's international hospital, Tokyo, Japan
Background

The European clinical guideline recommends using 30 mEq/L as the cut-off level of urine sodium (U-Na) to differentiate hypovolemic hyponatremia (hypo-Na) from others. However, due to the complexity of hyponatremia, we frequently encounter the patients whose U-Na are not completely suppressed and wonder the accuracy of this cut-off level. This study is to examine the diagnostic performance of U-Na and other parameters, and clarify optimal cut-off level of U-Na in patients with hyponatremia.

Methods

In this single-center, retrospective cohort study, we collected data of hospitalized patients with profound hypotonic hyponatremia evaluated by nephrology consultants, defined by serum Na (S-Na) ≦ 120 mEq/L and serum osmolality (Osm) ≦ 280 mOsm/kg H2O from April 2011 to September 2017. The final diagnosis of hyponatremia was categorized into either hypo-Na or SIADH based on nephrologist evaluation through the hospital course. Patients with urine Osm ≦ 100 mOsm/kg H2O or diagnosis of polydipsia, adrenal insufficiency and hypervolemia were excluded. The diagnostic accuracy of U-Na, fractional excretion of sodium (FENa), FE urea, and FE uric acid for hypo-Na were evaluated by receiver-operating characteristic (ROC) curves and the areas under the ROC curves (AUC).

Results

Of 130 patients (age 75.7 ± 13.1, 51% of males, minimal S-Na 115 ± 4.1 mEq/L), 97 patients (75%) were diagnosed as hypo-Na. In the ROC curves, U-Na showed the best diagnostic utility in differentiating hypo-Na and SIADH with AUC of 0.79 compared to FENa, FE urea and FE uric acid (AUC of 0.39, 0.44 and 0.50, respectively) (Figure). The optimal cut-off level of U-Na was 56 mEq/L with sensitivity of 64% and specificity of 90%, which was not significantly changed when assessed in patients with diuretics use (n=40) or not (n=90) with cut-off levels of 64 mEq/L and 56 mEq/L, respectively.

Conclusion

U-Na performed the best in differentiating hypo-Na and SIADH in hyponatremic patients with a cut-off level of 56 mEq/L, higher than that recommended in the current guidelines. The diagnostic accuracy was not influenced by diuretics use.

ROC curves of diagnostic parameters for hypo-Na