Polyuria

olyuria is generally defined as a urine production > 3L/day in adults and 2 L/m² body surface area in children. It is important to differentiate between polyuria and symptoms of frequent urination and nocturia (the need to urinate at night) where there is not necessarily an increased production of urine.

Causes of polyuria:

Osmotic diuresis - for example induced by glucose in badly controlled diabetes mellitus.

Primary polydipsia Also known as psychogenic polydipsia. The primary cause of the patient's polyuria is increased fluid intake. This is seen in combination with mental illnese and with patients that use medicines that lead to dry mouth. Diseases in the hypothalamus can damage the thirst center and lead to a primary polydipsia.

Central diabetes insipidus Also known as neurohypophyseal or neurogenic diabetes insipidus. The disease is caused by a defect in the excretion of antidiuretic hormone (ADH) and can be idiopathic, due to autoimmune damage to the ADH-producing cells, trauma, pituitary surgery or encephalopathy. There are also rare hereditary forms of central diabetes insipidus.

Nephrogenic diabetes insipidus: ADH-secretion is normal, while there is varying resistance to the effect of ADH in the kidneys. In children, it is alomst always a hereditary defect either in the ADH receptor (AVPR2-gene, X-linked recessive) or in the gene for the water channel aquaporin-2. In adults, nephrogenic diabetes insipidus is associated with cronic use of lithium or hypercalcemia. The disease can occur in a mild form in the elderly or together with another underlying kidney disease that leads to reduced ability to concentrate the urine.