Teaching Pearls:

• Can be categorized into the following:
  • Hyperosmolar
    • Hyperglycemia, mannitol use
  • Iso-osmolar
    • Hypertriglyceridemia, hyperparaproteinemia
  • Hypo-osmolar
• Hypo-osmolar hyponatremia can be divided into different categories based on volume status:
  • Hypovolemic
    • GI losses, diuretic use, blood loss
    • ↓↓salt/↓H2O
    • Urine osm >100mOsm/L
    • Urine Na <20 mmol/L
  • Euvolemic
    • siADH, psychogenic polydipsia, adrenal insufficiency, hypothyroidism, low solute intake (tea toast diet or beer potomania)
    • Salt/↑H2O
    • siADH
      • Urine osm >100mOsm/L
      • Urine Na >40 mmol/L
    • Psychogenic polydipsia
      • Urine osm<100mOsm/L
      • Urine Na >20mmol/L
  • Hypervolemic
    • CHF, nephrotic syndrome, cirrhosis
    • ↑Salt/↑↑H2O
    • Urine osm >100mOsm/L
    • Urine Na <20mmol/L
• Hypothyroidism presents as a hypoosmolar euvolemic hyponatremia.
  • Can present with a clinical picture and urine studies similar to siADH
  • Can also present as a picture of CHF.
    • Often these patients have myxedema coma.
    • Theorized that the decreased cardiac output leads to decreased glomerular filtration, leading to poor excretion of free water.
• Adrenal insufficiency commonly presents with hyponatremia, hyperkalemia, and metabolic acidosis.
• Low solute diet (tea toast diet and/or beer potomania)
  • Kidneys can dilute urine to as low as 50mOsm/L.
  • If intake of solute is very low, then it limits the amount of free water that can be excreted.
• For more teaching points, check out the hyponatremia section on http://www.professorebm.com.