Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1222 page)

   Cutaneous causes: burns or excessive sweating

   Drugs: infusion of hypertonic sodium salts, hypertonic saline, Na-bicarbonate; hypertonic dialysis

   Hyperaldosteronism, Cushing syndrome—rare causes

   Diabetes insipidus (DI)

   Posttraumatic: caused by tumors, cysts, histiocytosis, TB, sarcoidosis

   Idiopathic: caused by aneurysms, meningitis, encephalitis, Guillain–Barre syndrome

   Renal failure and other renal causes: loop diuretics, osmotic diuresis (glucose, urea, mannitol), postobstructive diuresis, polyuric, phase of acute tubular necrosis, intrinsic renal disease

Decreased In

   Hyponatremia (defined as serum sodium <135 mmol/L after the exclusion pseudohyponatremia). This can be classified as three types depending upon extracellular fluid (ECF) status.

   Hypovolemic hyponatremia (reduced ECF)

   Renal loss of Na and water: caused by diuretic use, salt-wasting nephropathy, cerebral salt wasting, adrenal insufficiency, renal tubular acidosis

   Extrarenal loss of Na and water with renal conservation: caused by burns, GI loss, pancreatitis, bowel obstruction, blood loss

   Hypervolemic hyponatremia (expanded ECF and ICF but reduced effective arterial blood volume): caused by CHF, cirrhosis, nephrotic syndrome

   Euvolemic hyponatremia (expanded ECF and ICF without edema: caused by thiazide diuretic use, hypothyroidism, adrenal insufficiency, SIADH secretion)