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A relatively common sign, polyuria is the daily production and excretion of more than 3 L of urine. It’s usually reported by the patient as increased urination, especially when it occurs at night. Polyuria is aggravated by overhydration, consumption of caffeine or alcohol, and excessive ingestion of salt, glucose, or other hyperosmolar substances. (See Polyuria: Common causes and associated findings, pages 492 and 493.)
Polyuria usually results from the use of certain drugs, such as a diuretic, or from a psychological, neurologic, or renal disorder. It can reflect central nervous system dysfunction that diminishes or suppresses antidiuretic hormone (ADH) secretion, which regulates fluid balance. Or, when ADH levels are normal, it can reflect renal impairment. In both of these pathophysiologic mechanisms, the renal tubules fail to reabsorb sufficient water, causing polyuria.
Because the patient with polyuria is at risk for developing hypovolemia, evaluate his fluid status first. Take his vital signs, noting an increased body temperature, tachycardia, and orthostatic hypotension (a ≥10 mm Hg decrease in systolic blood pressure upon standing and a ≥10 beats/minute increase in heart rate upon standing). Inspect for dry skin and mucous membranes, decreased skin turgor and elasticity, and reduced perspiration. Is the patient unusually tired or thirsty? Has he recently lost more than 5% of his body weight? If you detect these effects of hypovolemia, you’ll need to infuse replacement fluids.
If the patient doesn’t display signs of hypovolemia, explore the frequency and pattern of the polyuria. When did it begin? How long has it lasted? Was it precipitated by a certain event? Ask the patient to describe the pattern and amount of his daily fluid intake. Check for a history of visual deficits, headaches, or head trauma, which may precede diabetes insipidus. Also check for a history of urinary tract obstruction, diabetes mellitus, renal disorders, chronic hypokalemia or hypercalcemia, or psychiatric disorders (past and present). Find out the schedule and dosage of any drugs the patient is taking.
Perform a neurologic examination, noting especially any change in the patient’s level of consciousness. Then palpate the bladder and inspect the urethral meatus. Obtain a urine specimen and check its specific gravity.
During the diuretic phase of acute tubular necrosis, polyuria of less than 8 L/day gradually subsides after 8 to 10 days. Urine specific gravity (1.010 or less) increases as polyuria subsides. Related findings include weight loss, decreasing edema, and nocturia.
Polyuria of about 5 L/day with a specific gravity of 1.005 or less is common, although extreme polyuria — up to 30 L/day — occasionally occurs. Polyuria is commonly accompanied by polydipsia, nocturia, fatigue, and signs of dehydration, such as poor skin turgor and dry mucous membranes.
With diabetes mellitus, polyuria seldom exceeds 5 L/day, and urine specific gravity typically exceeds 1.020. The patient usually reports polydipsia, polyphagia, weight loss, weakness, frequent urinary tract infections and yeast vaginitis, fatigue, and nocturia. The patient may also display signs of dehydration and anorexia.
Polyuria gradually progresses to oliguria with chronic glomerulonephritis. Urine output is usually less than 4 L/day; specific gravity is about 1.010. Related GI findings include anorexia, nausea, and vomiting. The patient may experience drowsiness, fatigue, edema, a headache, elevated blood pressure, and dyspnea. Nocturia, hematuria, frothy or malodorous urine, and mild to severe proteinuria may occur.
After resolution of a urinary tract obstruction, polyuria — usually more than 5 L/day with a specific gravity of less than 1.010 — occurs for up to several days before gradually subsiding. Bladder distention and edema may occur with nocturia and weight loss. Occasionally, signs of dehydration appear.
Most common in people older than age 30, psychogenic polydipsia usually produces dilute polyuria of 3 to 15 L/day, depending on fluid intake. The patient may appear depressed and have a headache and blurred vision. Weight gain, edema, elevated blood pressure and, occasionally, stupor or coma may develop. With severe overhydration, signs of heart failure may present.
Transient polyuria can result from radiographic tests that use contrast media.
Diuretics characteristically produce polyuria. Cardiotonics, vitamin D, demeclocycline, phenytoin, lithium, methoxyflurane, and propoxyphene can also produce polyuria.
Maintaining adequate fluid balance is your primary concern when the patient has polyuria. Record his intake and output accurately, and weigh him daily. Closely monitor the patient’s vital signs to detect fluid imbalance, and encourage him to drink adequate fluids. Review his medications, and recommend modification where possible to help control symptoms.
Prepare the patient for serum electrolyte, osmolality, blood urea nitrogen, and creatinine studies to monitor fluid and electrolyte status and for a fluid deprivation test to determine the cause of polyuria.
The major causes of polyuria in children are congenital nephrogenic diabetes insipidus, medullary cystic disease, polycystic renal disease, and distal renal tubular acidosis.
Because a child’s fluid balance is more delicate than an adult’s, check his urine specific gravity at each voiding, and be alert for signs of dehydration. These include a decrease in body weight; decreased skin turgor; pale, mottled, or gray skin; dry mucous membranes; decreased urine output; and an absence of tears when crying.
In elderly patients, chronic polyuria is commonly associated with an underlying disorder. The possibility of associated malignant disease must be investigated.
Read excerpts from these other book chapters related to Weak urination:
Copyright Details: Handbook of Signs & Symptoms (Third Edition), Copyright © 2008 Williams & Wilkins.
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More About This Book:
Title: Handbook of Signs & Symptoms (Third Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2006 ISBN: 1-58255-402-1 
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