Polyuria

• Urine > 3.0 L/day
• Two potential mechanisms:
  • Solute diuresis: excretion of nonabsorbable solutes (such as glucose)
  • Water diuresis: excretion of water (usually from a defect in ADH production or renal responsiveness)
• To distinguish between the above two, urine osmolality is measured.

Approach by osmolality:

<250 mosmol	History, low S.Na	Primary polydipsia Psychogenic Hypothalamic disease Drugs (thioridazine, chlorpromazine, anticholinergic agents)
	Water deprivation test or ADH level
	Diabetes insipidus (DI)	Central DI (vasopressin-sensitive) posthypophysectomy, trauma, supra- or intrasellar tumor / cyst histiocystosis or granuloma, encroachment by aneurysm, Sheehans syndrome, infection, Guillain-Barré, fat embolus, empty sella
		Nephrogenic DI (vasopressin-insensitive) Acquired tubular diseases: pyelonephritis, analgesic nephropathy, multiple myeloma, amyloidosis, obstruction, sarcoidosis, hypercalcemia, hypokalemia, Sjögren’s syndrome, sickle cell anemia Drugs or toxins: lithium, demeclocycline, methoxyflurane, ethanol, diphenylhydantoin, propoxyphene, amphotericin Congenital: hereditary, polycystic or medullary cystic disease
>300 mosmol	Solute diuresis Glucose, mannitol, radiocontrast, urea (from high protein feeding), medullary cystic diseases, resolving ATN, or obstruction, diuretics