Polyuria is a condition usually defined as excessive or abnormally large production or passage of urine (at least 2.5 or 3 L over 24 hours in adults). Frequent urination is sometimes included by definition, but is nonetheless usually an accompanying symptom. Increased production and passage of urine may also be termed diuresis.
Polyuria often appears in conjunction with polydipsia (increased thirst), though it is possible to have one without the other, and the latter may be a cause or an effect. Psychogenic polydipsia may lead to polyuria.
The most common cause of polyuria in both adults and children is uncontrolled diabetes mellitus, causing an osmotic diuresis. In the absence of diabetes mellitus, the most common causes are excessive secretion of aldosterone due to adrenal cortical tumor,primary polydipsia (excessive fluid drinking), central diabetes insipidus and nephrogenic diabetes insipidus.
Polyuria may also be due to various chemical substances (diuretics, caffeine, ethanol). It may also occur after supraventricular tachycardias, during an onset of atrial fibrillation, childbirth, and the removal of an obstruction within the urinary tract. Diuresis is restrained by antidiuretics such as ADH,angiotensin II and aldosterone.
Cold diuresis is the occurrence of increased urine production on exposure to cold, which also partially explains immersion diuresis.
Substances that increase diuresis are called diuretics.
Substances that decrease diuresis allow more vasopressin or antidiuretic hormone (ADH) to be present in the kidney.
High-altitude diuresis occurs at altitudes above 10,000 ft and is a desirable indicator of adaptation to high altitudes. Mountaineers who are adapting well to high altitudes experience this type of diuresis. Persons who produce less urine even in the presence of adequate fluid intake probably are not adapting well to altitude.