ASN's Mission

To create a world without kidney diseases, the ASN Alliance for Kidney Health elevates care by educating and informing, driving breakthroughs and innovation, and advocating for policies that create transformative changes in kidney medicine throughout the world.

learn more

Contact ASN

1401 H St, NW, Ste 900, Washington, DC 20005


The Latest on Twitter

Kidney Week

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


  • 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

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.


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).


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.


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