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).

• Nocturnal polyuria (NP), characterized by overproduction of urine at night (more than 20%-33% of total 24-hour urine volume depending on age). It can be caused by intake, urological, nephrological, hormonal, sleep, and cardiovascular factors.

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

• Diagnostic Approach

Suspected hypotonic polyuria

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

(Polyuria confirmed): Measure urine osmolality

(No polyuria/ or >800 mOsm/kg): 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): Primary polydipsia

Normal serum Sodium/plasma osmolality: Indeterminate diagnosis

High serum Sodium (>146 mmol/L), plasma osmolality (>300 mOsm/kg): 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): Therapeutic trial with desmopressin

Nephrogenic DI(partial or complete)

Complete Central DI

Primary polydipsia

Partial Nephrogenic DI

Partial Central DI

(Initial urine osmolality: 30 mOsm/kg and >50% increase after desmopressin): Complete Central DI

(Urine osmolality <300 mOsm/kg or <50% increase): Complete Nephrogenic DI

Polyuria ❑ 24-hour urine volume >3L ❑ 24-hour urine volume >50 ml/kg

Urine Osmolality >300mosmol

Urine Osmolality <300mosmol

Solute diuresis ❑ Glucose ❑ Mannitol ❑ Contrast media ❑ High protein intake ❑ Diuretics ❑ Medullary cystic disease ❑ Resolving ATN ❑ Resolving obstruction

Water diuresis ❑ Primary polydipsia ❑ Diabetes inspidous

Water restriction test OR administration of hypertonic saline 0.05 mL/kg/min for 2 h

Water restriction test ❑ Overnight fluid restriction should be avoided ❑ Recommend the patient to stop drinking 2-3 hours before coming to clinic ❑ Meaure urine volume every hour ❑ Measure urine osmolality every hour ❑ Measure plasma sodium concentration every 2 hours ❑ Measure plasma osmolality every 2 hours

Test endpoints in adults: ❑ Urine osmolality reaches normal value (above 600 mosmol/kg)[means that ADH release and effect are intact] ❑ The urine osmolality is stable for 2 or 3 successive hourly measurements despite a rising plasma osmolality ❑ Plasma osmolality >295-300 mosmol/kg ❑ Plasma sodium is 145 or higher

In the last 3 settings desmopressin 10mcg intranasal, or 4mcg SC/IV is administered ❑ Measure urine volume and urine osmolality every 30 minutes over the next two hours

>100% rise in urine osmolality

15-50% rise in urine osmolality after administration of exogenous desmopressin

<15% rise in urine osmolality

Complete central diabetes inspidous

Partial central DI or partial nephrogenic DI

complete nephrogenic DI or '''primary polydipsia'''

Check plasma and urine ADHand copeptin prior to administration of exogenous ADH ❑ Increase in plasma/urine ADH in response to rising plasma osmolality excludes central DI ❑ Appropriate elevation in urine osmolality as ADH secretion is increased excludes nephrogenic DI ❑ Copeptin > 21.4 picomol/L differentiates Nephrogenic DI from other etiologies with 100% sensivity and specifity