Fluid deprivation test Fluid deprivation test A fluid or water deprivation test is a medical test which can be used to determine whether the patient has diabetes insipidus as opposed to other causes of polydipsia (a condition of excessive thirst that causes an excessive intake of water). The patient is required, for a prolonged period, to forgo intake of water completely, to determine the cause of the thirst. This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of ADH (a synonym for vasopressin) during this test is also necessary. If there is
Primary polydipsia Primary polydipsia Primary polydipsia is a form of polydipsia characterised by excessive fluid intake in the absence of physiological stimuli to drink. This includes psychogenic polydipsia (PPD – not to be confused with postpartum depression), which is caused by psychiatric disorders, often schizophrenia, and often accompanied by the sensation of dry mouth. Some forms of primary polydipsia are explicitly non-psychogenic. Primary polydipsia is a diagnosis of exclusion. In diagnosis, primary polydipsia is usually categorised as: The terms primary polydipsia and psychogenic polydipsia are sometimes incorrectly used interchangeably – to be considered psychogenic, the patient needs to have some other psychiatric