Polyuria resident survival guide

Overview

• Polyuria is defined as urine output more than 2 L/24 hours, or 30 ml/kg/24 hours. There are 3 pathophysiologic causes of polyuria: increased thirst (idiopathic, psychogenic polydepsia, hypothalamic disease, and medications), central diabetes insipidus (DI) (decreased secretion of arginine vasopressin (AVP)), and nephrogenic diabetes insipidus (DI) (renal resistance to AVP).

Causes

Life Threatening Causes

• Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.
• Polyuria does not have life threatening causes.

Common causes

• The most common causes of polyuria are:
  • Pregnancy
  • Psychogenic polydipsia
  • Central diabetes insipidus (CDI)
  • Nephrogenic diabetes insipidus (NDI)
  • Diabetes mellitus (DM)
  • Chronic kidney disease (CKD)
  • Urinary tract infection (UTI)
  • Interstitial cystitis
  • Nephrolithiasis
  • Primary hyperparathyroidism
  • Familial hypocalciuric hypercalcemia
  • Hypercalcemia
  • Hypokalemia
  • Sickle cell disease (SCD)
  • Stroke or neurological diseases
  • Benign prostatic hyperplasia (BPH)
  • Stress incontinence
  • Medications:
    • Lithium
    • diuretics
  • Overactive bladder
  • Drinking alcohol or caffeine

Management

Shown below is an algorithm summarizing the approach to polyuria.

Suspected hypotonic polyuria

Confirm presence of polyuria: >50ml/kg/24hrs or >3-4L/day

Polyuria confirmed:

No polyuria/ or >800 mOsm/kg:

Measure urine osmolality

Diabetes insipidus(DI)/Primary polydipsia ruled out

<800 mOsm/kg:

Hypotonic polyuria confirmed:

Measure serum Sodium and plasma osmolality

Low normal or low serum Sodium <150 mmol/L, plasma osmolality <280 mOsm/kg:

Normal serum Sodium/plasma osmolality:

High serum Sodium >146 mmol/L, plasma osmolality >300 mOsm/kg:

Primary polydipsia

Indeterminate diagnosis

Central or Nephrogenic DI

Water deprivation test

Baseline plasma copeptin

Hypertonic saline infusion test

Urine Osm >800 mOsm/kg

Urine Osm <300 mOsm/kg

Urine Osm 300-800 mOsm/kg

Plasma coprptin >4.9pmol/L

Plasma coprptin <4.9pmol/L

Mild primary polyuria

Desmopressin administration

>21pmol/L

<2.6pmol/L

>2.6pmol/L

Urine Osmolality: 300-800 mOsm/Kg and <50% increase:

Nephrogenic DI(partial or complete)

Complete Central DI

Therapeutic trial with desmopressin

Primary polydipsia

Partial Nephrogenic DI

Partial Central DI

Initial urine osmolality: 30 mOsm/kg and >50% increase after desmopressin:

Urine osmolality <300 mOsm/kg or <50% increase:

Complete Central DI

Complete Nephrogenic DI

Polyuria (Urine Output > 3L/d)

Urine Osmolality

Uosm <100mOsm/kg (Water Diuresis) *Psychogenic Polydipsia *DI (central and nephrogenic)

Uosm =100-300mOsm (Mixed Polyuria) *Partial DI(central and Nephrogenic) *Simultaneous water and solute intake *CKD

Uosm >300mOsm/kg (Solute Diuresis) *Hyperglycemia *Azotemia *High solute intake intravenous fluids enteral and parenteral nutrition Exogenous supplements

Water Deprivation Test

24-Hour Urine Collection (estimation of osmoles) *Urine sodium *Urine potassium *Urine glucose *Urine urea nitrogen *Other osmoles

Do's

• Recommend diet modification, like avoiding any food that irritates bladder including caffeine, alcohol, carbonated drinks, tomato-based products, chocolate, artificial sweeteners, and spicy foods.
• Monitor fluid food intake, drink enough to prevent constipation and over concentration of urine and avoid drinking just before the bedtime.
• Recommend Kegel exercises to strengthen the muscles around the bladder and urethra.