Excessive Thirst & Urination in Adults: Definitions & Causes

Polydipsia (excessive thirst): >3 L/day fluid intake.
Polyuria (excessive urine output): >3 L/day urine volume.

Common Causes

1. Diabetes mellitus – Hyperglycemia → osmotic diuresis → polyuria → polydipsia.
2. Diabetes insipidus – Central (ADH deficiency) or nephrogenic (ADH resistance); dilute urine, extreme thirst.
3. Chronic kidney disease – Loss of concentrating ability.
4. Primary polydipsia (psychogenic) – Compulsive water drinking; urine dilute.
5. Medications – Diuretics, lithium, demeclocycline, SGLT2 inhibitors.
6. Hypercalcemia – Nephrogenic DI.
7. Hypokalemia – Impairs concentrating ability.
8. Endocrine – Hyperthyroidism, Cushing's, Addison's (salt wasting).
9. SIADH – Usually causes hyponatremia with concentrated urine; but reset osmostat can mimic.

Diagnostic Approach

• Serum glucose, Na⁺, osmolality, Ca²⁺, K⁺
• Urine osmolality, Na⁺, glucose
• Water deprivation test (for DI)
• ADH/copeptin levels

See a physician for evaluation; untreated causes can lead to dehydration, electrolyte emergencies, or renal damage.