Causes of Polyuria - Differential Diagnosis Algorithm

Polyuria - Urine Output > 3L/day, Increased Urine Volume (>2ml/min)

Osmotic Diuresis

Urine Osmolality > Serum Osmolality

 • Hyperglycemia (Uncontrolled Diabetes Mellitus)

 • Mannitol administration

 • Increased urea concentration (e.g. Recovery from Acute Renal Failure, increased protein feeds, Hypercatabolism [Burns, Steroids], GI Bleed)

 • NaCl administration

Hypertonic Urine Following Water Deprivation Test

 • Primary polydipsia

Hypotonic Urine Following Water Deprivation Test - Excessive Loss

 - DDAVP -> Uosm Increased by >50% - Proper kidney response

     • Central Diabetes Insipidus

 - DDAVP -> Uosm unchanged or increased by <50% - Unresponsive Kidney

     • Nephrogenic Diabetes Insipidus



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