Most people urinate about 4 to 6 times a day, mostly in the daytime. Normally, adults pass between 3 cups (700 milliliters) and 2 quarts (2 liters) of urine a day. Infants may pass as little as 1 cup (230 milliliters) per day. Urination can be increased if a person produces an excess volume of urine or produces a normal volume of urine but feels the need to go more often (urinary frequency).

Causes

Increased Volume: Excess urine can be caused by drinking too much fluid (polydipsia), by taking diuretic drugs or substances that have a diuretic effect, such as alcohol or caffeine, or by having a high level of sugar in the blood (as in diabetes mellitus). A rare condition called diabetes insipidus causes excess urine because of problems with a brain hormone called antidiuretic hormone (also called vasopressin). Antidiuretic hormone helps the kidney reabsorb fluid. If too little antidiuretic hormone is produced (a condition called central diabetes insipidus—see Pituitary Gland Disorders: Central Diabetes Insipidus) or if the kidney is unable to properly respond to it (nephrogenic diabetes insipidus—see Tubular and Cystic Kidney Disorders: Nephrogenic Diabetes Insipidus), the person urinates excessively.

Increased Frequency: A frequent need to urinate without an increase in the total daily output of urine can occur when something irritates or presses on the bladder. A urinary tract infection (UTI) is the most common cause of bladder irritation. Rarer causes include a stone or tumor in the bladder. A tumor or other mass (or even the uterus if a woman is pregnant) pressing on the outside of the bladder can also cause a frequent urge to urinate because the mass reduces the capacity of the bladder. An inability to fully empty the bladder because of partial obstruction, often from an enlarged prostate (in men), can cause frequency.

Evaluation and Treatment

The doctor asks about the use of diuretics. Symptoms such as pain or burning may indicate infection. For men, the doctor examines the prostate by putting a gloved, lubricated finger in the man's rectum. If the prostate is enlarged, a blood test (prostate specific antigen, or PSA, test) and sometimes prostate ultrasonography are done. The doctor usually checks the urine for glucose (suggesting diabetes mellitus) and bacteria or excess white blood cells (indicating infection). If the cause is not clear, the doctor may measure levels of electrolytes in the blood and urine and sometimes may do imaging tests of the kidney, ureters, or bladder (such as computed tomography [CT], ultrasonography, or magnetic resonance imaging [MRI]).

Treatment is directed at the underlying disorder.

Last full review/revision March 2007 by Ralph E. Cutler, MD