Polyuria: Definition, Causes, and Clinical Approach

Polyuria = urine output >2.5–3 L/24h in adults. Distinguish from urinary frequency (normal volume, frequent voids) and nocturia.

Major Etiologies

• Diabetes mellitus (osmotic diuresis from glucosuria).
• Diabetes insipidus (central: ADH deficiency; nephrogenic: renal ADH resistance).
• Primary polydipsia (psychogenic or habitual excessive intake).
• Diuretic use (loop, thiazide, SGLT2 inhibitors).
• Hypercalcemia / Hypokalemia (impair concentrating ability).
• Chronic kidney disease (loss of medullary gradient).

Workup

24-h urine volume, simultaneous serum/urine osmolality, glucose, calcium, electrolytes. Water deprivation test + desmopressin challenge if DI suspected.

Treatment targets the underlying disorder.