What is polyuria
Polyuria is urine output of more than 2.5 to 3 L/day; polyuria must be distinguished from urinary frequency, which is the need to urinate many times during the day or night but in normal or less-than-normal volumes. Either problem can include nocturia. Normal urine production in an adult is 1 to 2 liters/day. Urine volume is influenced by factors such as fluid intake, blood pressure, dietary habits, temperature, medications, mental state and general health. As people age, their kidneys become less effective and urinary symptoms become more common. Polyuria is a fairly common symptom which is often noticed when it occurs at night. People often notice the problem when they have to get up during the night to use the bathroom (nocturia). Polyuria is often accompanied by excessive fluid intake (polydipsia).
Some common causes of polyuria are:
- Diabetes insipidus
- Diabetes mellitus
- Drinking excessive amounts of water
To monitor your urine output, keep a daily record of the following:
- How much you drink
- How often you urinate and how much urine you produce each time
- How much you weigh (use the same scale every day)
The most common cause of polyuria in adults is:
- Taking diuretics (water tablets)
The most common cause of polyuria in adults and children is:
- Uncontrolled diabetes mellitus
In the absence of diabetes mellitus, the most common causes are:
- Primary polydipsia
- Central diabetes insipidus
- Nephrogenic diabetes insipidus
Less common causes include:
- Kidney failure
- Medicine such as lithium
- High or low calcium level in the body
- Drinking alcohol and caffeine
- Sickle cell anemia
Also, your urine production may increase for 24 hours after having tests that involve injecting a special dye (contrast medium) into your vein during imaging tests such as a CT scan or an MRI scan.
Polyuria is you pass urine of more than 2.5 to 3 L/day.
Your provider will perform a physical exam and ask questions such as:
- When did the problem start and has it changed over time?
- How often do you urinate? Do you get up at night to urinate?
- Do you have problems controlling your urine?
- What makes the problem worse? Better?
- Have you noticed any blood in your urine or change in urine color?
- Do you have any other symptoms (such as pain, burning, fever, or abdominal pain)?
- Do you have a history of diabetes, kidney disease, or urinary infections?
- What medicines do you take?
- How much salt do you eat? Do you drink alcohol and caffeine?
Tests that may be done include:
- Blood sugar (glucose) test
- Blood urea nitrogen test
- Creatinine (serum)
- Electrolytes (serum)
- Fluid deprivation test (limiting fluids to see if the urine volume decreases)
- Osmolality blood test
- Urine osmolality test
- 24-hour urine test
These tests look for hypercalcemia, hypokalemia (due to surreptitious diuretic use), and hypernatremia or hyponatremia:
- Hypernatremia (sodium > 142 mEq/L) suggests excess free water loss due to central or nephrogenic diabetes insipidus.
- Hyponatremia (sodium < 137 mEq/L) suggests excess free water intake secondary to polydipsia.
- Urine osmolality is typically < 300 mOsm/kg with water diuresis and > 300 mOsm/kg with solute diuresis.
If the diagnosis remains unclear, then measurement of serum and urine sodium and osmolality in response to a water deprivation test and exogenous ADH administration should be done. Because serious dehydration may result from this testing, the test should be done only while patients are under constant supervision; hospitalization is usually required. Additionally, patients in whom psychogenic polydipsia is suspected must be observed to prevent surreptitious drinking.
Various protocols can be used in water deprivation tests. Each protocol has some limitations. Typically, the test is started in the morning by weighing the patient, obtaining venous blood to determine serum electrolyte concentrations and osmolality, and measuring urine osmolality. Voided urine is collected hourly, and its osmolality is measured. Dehydration is continued until orthostatic hypotension and postural tachycardia appear, ≥ 5% of the initial body weight has been lost, or the urinary concentration does not increase > 30 mOsm/kg in sequentially voided specimens. Serum electrolytes and osmolality are again determined, and 5 units of aqueous vasopressin are injected sc. Urine for osmolality measurement is collected one final time 60 min postinjection, and the test is terminated.
A normal response produces maximum urine osmolality after dehydration (> 700 mOsm/kg), and osmolality does not increase more than an additional 5% after injection of vasopressin.
In central diabetes insipidus, patients are typically unable to concentrate urine to greater than the plasma osmolality but are able to increase their urine osmolality after vasopressin administration. The increase in urine osmolality is 50 to 100% in central diabetes insipidus vs 15 to 45% with partial central diabetes insipidus.
In nephrogenic diabetes insipidus, patients are unable to concentrate urine to greater than the plasma osmolality and show no additional response to vasopressin administration. Occasionally in partial nephrogenic diabetes insipidus, the increase in urine osmolality can be up to 45%, but overall these numbers are much lower than those that occur in partial central diabetes insipidus (usually < 300 mOsm/kg).
In psychogenic polydipsia, urine osmolality is < 100 mOsm/kg. Decreasing water intake gradually will lead to decreasing urine output, increasing plasma and urine osmolality and serum sodium concentration.
Measurement of circulating ADH (anti-diuretic hormone) is the most direct method of diagnosing central diabetes insipidus. Levels at the end of the water deprivation test (before the vasopressin injection) are low in central diabetes insipidus and appropriately elevated in nephrogenic diabetes insipidus. However, ADH levels are not routinely available. In addition, water deprivation is so accurate that direct measurement of ADH is rarely necessary. If measured, ADH levels should be checked at the beginning of the water deprivation test, when the patient is well hydrated; ADH levels should increase as intravascular volume decreases.
Treatment depends on the cause of polyuria.