Polyuria

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: Causes and associated findings.)

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 secretion of antidiuretic hormone (ADH), 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.

History and physical examination

Because the patient with polyuria is at risk for developing hypovolemia, evaluate fluid status first. Take vital signs, noting increased body temperature, tachycardia, and orthostatic hypotension (a 10-mm Hg decrease in systolic blood pressure upon standing and a 10-beats per 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 disorder, chronic hypokalemia or hypercalcemia, or psychiatric disorder (both 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.

Medical causes

Acute tubular necrosis

During the diuretic phase of this disorder, 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.

Diabetes insipidus

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.

Diabetes mellitus

With this disorder, 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.

Glomerulonephritis (chronic)

Polyuria gradually progresses to oliguria with this disorder. 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, headache, elevated blood pressure, and dyspnea. Nocturia, hematuria, frothy or malodorous urine, and mild to severe proteinuria may occur.

Hypercalcemia

Elevated plasma calcium levels may lead to nephropathy, usually producing polyuria of less than 5 L/day with a specific gravity of about 1.010. Accompanying signs and symptoms include polydipsia, nocturia, constipation, paresthesia and, occasionally, hematuria, and pyuria. With severe hypercalcemia, the patient’s condition worsens rapidly and he experiences anorexia, vomiting, stupor progressing to coma, and renal failure.

Hypokalemia

Prolonged potassium depletion may lead to nephropathy, which results in polyuria—usually less than 5 L/day with a specific gravity of about 1.010. Associated findings include polydipsia, circumoral and foot paresthesia, hypoactive deep tendon reflexes, fatigue, hypoactive bowel sounds, nocturia, arrhythmias, and muscle cramping, weakness, or paralysis.

Postobstructive uropathy

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.

Psychogenic polydipsia

Most common in those older than age 30, this disorder 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.

Pyelonephritis

Acute pyelonephritis usually results in polyuria of less than 5 L/day with a low but variable specific gravity. Other findings include persistent high fever, flank pain (usually unilateral), hematuria, costovertebral angle tenderness, chills, weakness, dysuria, urinary frequency and urgency, tenesmus, and nocturia. Occasionally, nausea, anorexia, vomiting, and hypoactive bowel sounds occur.

Chronic pyelonephritis produces polyuria of less than 5 L/day that declines as renal function worsens. Urine specific gravity is usually about 1.010 but may be higher if proteinuria is present. Other effects include irritability, paresthesia, fatigue, nausea, vomiting, diarrhea, drowsiness, anorexia, pyuria and, in late stages, elevated blood pressure.

Sheehan’s syndrome

This syndrome of postpartum pituitary necrosis may cause polyuria of over 5 L/day with a specific gravity of 1.001 to 1.005. Associated findings include polydipsia, nocturia, and fatigue. Reproductive effects include failure to lactate, amenorrhea, decreased pubic and axillary hair growth, and reduced libido.

Sickle cell anemia

This disorder may cause nephropathy, typically producing polyuria of less than 5 L/day with a specific gravity of about 1.020. Additional findings include polydipsia, fatigue, abdominal cramps, arthralgia, priapism and, occasionally, leg ulcers, and bony deformities.

Other causes

Diagnostic tests

Transient polyuria can result from radiographic tests that use contrast media.

Drugs

Diuretics characteristically produce polyuria. Cardiotonics, vitamin D, demeclocycline, phenytoin, lithium, and propoxyphene can also produce polyuria.

Special considerations

Maintaining adequate fluid balance is your primary concern when the patient has polyuria. Record 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.

Pediatric pointers

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 absence of tears when crying.

Geriatric pointers

In elderly patients, chronic pyelonephritis is commonly associated with an underlying disorder. The possibility of associated malignant disease must be investigated.

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Book Source Details

• Book Title: Professional Guide to Signs & Symptoms (Fifth Edition)
• Author(s): Springhouse
• Year of Publication: 2006
• Copyright Details: Professional Guide to Signs & Symptoms (Fifth Edition), Copyright © 2006 Lippincott Williams & Wilkins.

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