Teaching Pearls:

• In the setting of normal renal and endocrine function, you can utilize your urine studies to help determine the etiology of Hyponatremia
• If Urine osmolality is low, consider the following two etiologies:
  • Primary polydipsia
    • Clinical history becomes important to differentiate.
  • Low solute diet (tea toast diet, beer potomania)
    • Clinical history becomes important to differentiate.
• If urine osmolality is high, this suggests an abnormal feature as kidneys would normally increase free water excretion.
  • Check urine sodium. If high, consider:
    • medication use (SSRI), hypothyroidism, adrenal insufficiency, siADH (if others ruled out).
  • If low, then renal perfusion appears to be poor. This can be seen in some of the following conditions:
    • True hypovolemia
    • Hypervolemic states including CHF (cardiorenal syndrome), cirrhosis, etc