Polyuria

Background

• Polyuria is defined as excessive urine output: >3 L/day in adults or >2 L/m² in children
• Distinguish from urinary frequency, which may not produce high volumes of urine
• In the ED, polyuria is usually secondary to an identifiable cause (hyperglycemia, medication effect, post-obstructive diuresis)
• Key EM consideration: assess for volume depletion and electrolyte derangements resulting from excessive urination
• May be an early presentation of diabetic ketoacidosis, HHS, or diabetes insipidus

Clinical Features

History

• Volume and frequency of urination
• Polydipsia (excessive thirst) — present in both diabetes mellitus and diabetes insipidus
• Duration of symptoms (acute vs. chronic)
• Medication review: diuretics, lithium, mannitol
• Associated symptoms: weight loss, fatigue (diabetes mellitus), confusion, lethargy (severe dehydration)
• Nocturia (waking to urinate at night)
• Recent urinary obstruction or catheter removal (post-obstructive diuresis)
• Psychiatric history (psychogenic polydipsia)
• Neurologic symptoms (central DI from pituitary pathology)

Physical Exam

• Assess volume status: orthostatic vital signs, mucous membranes, skin turgor, capillary refill
• Mental status (dehydration, hypercalcemia, hyperglycemia)
• Abdominal exam for bladder distension
• Signs of underlying endocrine disease

Differential Diagnosis

Osmotic Diuresis

• Hyperglycemia (DKA, HHS)
• Mannitol
• Urea diuresis
• Post-obstructive diuresis
• IV contrast (recent)

Water Diuresis

• Central diabetes insipidus: pituitary surgery, traumatic brain injury, tumor, infiltrative disease
• Nephrogenic diabetes insipidus: lithium, hypercalcemia, hypokalemia, chronic kidney disease
• Psychogenic polydipsia (primary polydipsia)

Drug-Induced

• Diuretics, caffeine, acetazolamide, lithium
• SGLT-2 inhibitors (glycosuria)
• Alcohol (suppresses ADH)

Other

• Hypercalcemia
• Hypokalemia
• Cushing's syndrome, primary hyperaldosteronism
• Inability to concentrate urine: chronic pyelonephritis, sickle cell disease
• Early renal failure
• Excess IV fluids

Evaluation

Polyuria evaluation algorithm.

Immediate

• Assess for dehydration and hemodynamic stability
• Bedside glucose (rule out hyperglycemia immediately)

Laboratory

• BMP: glucose, sodium, potassium, calcium, creatinine, BUN
• Urinalysis: glucosuria (diabetes mellitus), specific gravity, osmolality
• Serum osmolality
• Urine osmolality and urine electrolytes
• Consider:
  • Serum ADH level (if diabetes insipidus suspected)
  • Serum calcium, TSH
  • HbA1c if new hyperglycemia
  • Lithium level (if on lithium)

Distinguishing Water Diuresis from Osmotic Diuresis

• Urine osmolality >300 mOsm/kg: osmotic diuresis (hyperglycemia, mannitol, urea)
• Urine osmolality <300 mOsm/kg: water diuresis (diabetes insipidus, psychogenic polydipsia)
• In diabetes insipidus: serum osmolality elevated, urine dilute
• In psychogenic polydipsia: serum osmolality low-normal, urine dilute

Imaging

• Consider brain MRI if central diabetes insipidus suspected (pituitary pathology)
• Renal ultrasound if concern for obstruction or structural renal disease

Management

General

• Correct volume depletion with IV fluids
• Correct electrolyte abnormalities (especially sodium, potassium)
• Monitor urine output and replace losses if significant

Condition-Specific

• Hyperglycemia/DKA/HHS: insulin, IV fluids, electrolyte replacement (see DKA, HHS)
• Post-obstructive diuresis: monitor closely; replace urine output with IV fluids if hemodynamically significant (typically 0.5x urine output with NS); watch for electrolyte derangements
• Central diabetes insipidus: desmopressin (DDAVP), endocrinology consultation
• Nephrogenic diabetes insipidus: treat underlying cause, thiazide diuretics paradoxically reduce urine output, NSAIDs
• Lithium-induced DI: consider amiloride; nephrology consultation
• Psychogenic polydipsia: fluid restriction, psychiatric consultation

Disposition

Admit

• Hemodynamically unstable from volume depletion
• DKA or HHS
• Severe electrolyte derangements (hyper/hyponatremia, hypokalemia)
• New central diabetes insipidus (evaluate for intracranial pathology)
• Post-obstructive diuresis requiring close monitoring

Discharge

• Mild medication-induced polyuria with stable electrolytes
• Known diabetes insipidus at baseline with adequate desmopressin supply
• Mild hyperglycemia with appropriate outpatient follow-up
• Return precautions: persistent excessive thirst/urination, dizziness, confusion, inability to keep up with fluid intake

See Also

• Diabetes insipidus
• Diabetic ketoacidosis
• HHS
• Hyperglycemia
• Dehydration