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For further information, see CMDT Part 21-02: Hyponatremia

Key Features

  • A diagnosis of exclusion

  • Euvolemic hyponatremia

  • Other causes of hyponatremia should be ruled out, including

    • Low effective circulating volume

    • Decreased solute intake

    • Cortisol deficiency

    • Severe hypothyroidism

  • See Hyponatremia

Clinical Findings

  • Characterized by

    • Hyponatremia

    • Decreased plasma osmolality (< 280 mOsm/kg)

    • Euvolemia

    • Absence of heart, kidney, or liver disease

    • Normal thyroid and adrenal function

    • Urine sodium usually > 20 mEq/L


  • Clinical

  • Patients with SIADH may have low blood urea nitrogen (BUN) (< 10 mg/dL [3.6 mmol/L]) and hypouricemia (< 4 mg/dL [238 mcmol/L]), which are not only dilutional but result from increased urea and uric acid clearances in response to the volume-expanded state


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