Polyuria

Polyuria: Excerpt from In a Page: Signs and Symptoms

Polyuria is defined as urine output greater than 3 L per day. The output of a large volume of dilute urine leads to extracellular dehydration, which stimulates the thirst centers to influence the patient to increase fluid intake; thus, this condition may also lead to polydipsia.

Differential Diagnosis

• Diuretic use
• Primary polydipsia
  –Usually in middle-aged, anxious women
  –Psychiatric illnesses due to increased water intake (e.g. psychogenic polydipsia)
  –May be due to hypothalamic lesions in the thirst centers (e.g., sarcoidosis)
• Chronic lithium use
  –20% of patients develop polydipsia
• Central diabetes insipidus
  –Due to decreased output of antidiuretic hormone
  –May be idiopathic, familial, autoimmune, or due to head trauma, infiltrative diseases (e.g., sarcoidosis, granulomas, Langerhans cell histiocytosis), pituitary tumors (intrasellar, suprasellar), or ischemic or hypoxic encephalopathy
• Nephrogenic diabetes insipidus
  –Due to decreased response of the kidneys to antidiuretic hormone
  –May be idiopathic, familial, or due to drugs (e.g., colchicine, fluoride, phenothiazine), chronic renal disease, hypercalcemia, hypokalemia, sickle cell disease
• Uncontrolled diabetes mellitus
  –Patients have polydipsia and subsequent polyuria secondary to high sugar levels

Workup and Diagnosis

• Complete history and physical exam with corroboration from caretakers and family if available
• Initial laboratory studies include serum and urine fasting glucose, creatinine, electrolytes, osmolality, and serum BUN
• Water deprivation test
  –Give no fluids for 12–18 hours and measure body weight, plasma and urine osmolarity, blood pressure, and urine specific gravity every 2 hours
  –Stop test if severe dehydration or drop in BP occurs (indicates diabetes insipidus likely)
  –A normal response is a drop in urine output to 0.5 mL/min, and urine osmolarity >plasma osmolarity
  –Maintenance of dilute urine with specific gravity <1.005 indicates diabetes insipidus (central or nephrogenic)
  –Continue test until plateau phase (hourly increase UOP <30 mOsm/kg for 3 consecutive hours)
  –Then give 5 mg ADH SQ and measure urine osmolarity 1 hour later
• Measure ADH and osmolarity levels during water test
  –Nephrogenic diabetes insipidus: Normal or slightly increased ADH; urine osmolality increases <50% after ADH given
  –Complete central diabetes insipidus: Decreased levels of ADH; urine osmolarity >plasma osmolarity
  –Primary polydipsia: Serum and urine osmolarity are decreased before the test and increase during the water deprivation test

Treatment

• Central diabetes insipidus: Intranasal or oral DDAVP (a synthetic analog of ADH); must measure serum osmolarity and sodium levels regularly
• Nephrogenic diabetes insipidus: Control the underlying cause; diuretics and dietary salt restriction can decrease solute load to the kidney and keep a mild sodium depletion so there is increased proximal tubular resorption; polydipsia and increased urine output is generally mild in the elderly and patients with chronic renal failure
• Primary polydipsia: Limit water intake; this can be difficult especially if the cause is psychogenic
• Diabetes mellitus: Control sugar levels with oral medications or insulin
• Hypercalcemia and hypokalemia must be corrected and the underlying cause should be sought and treated
• Eliminate causative medications if possible

Book Source Details

• Book Title: In a Page: Signs and Symptoms
• Author(s): Scott Kahan, Ellen G. Smith
• Year of Publication: 2004
• Copyright Details: In a Page: Signs and Symptoms, Copyright © 2004 Lippincott Williams & Wilkins.

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: In a Page: Signs and Symptoms Authors: Scott Kahan, Ellen G. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2004 ISBN: 1-4051-0368-X

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