Fluid deprivation test
Encyclopedia
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 no change in the water loss despite fluid deprivation, desmopressin
may be administered to distinguish between the two types of diabetes insipidus
which are central & nephrogenic diabetes insipidus.
The time of deprivation may vary from 4 to 18 hours.
The serum osmolality and urine osmolality are both measured in the test.
Medical test
A diagnostic test is any kind of medical test performed to aid in the diagnosis or detection of disease. For example:* to diagnose diseases, and preferably sub-classify it regarding, for example, severity and treatability...
which can be used to determine whether the patient has diabetes insipidus
Diabetes insipidus
Diabetes insipidus is a condition characterized by excessive thirst and excretion of large amounts of severely diluted urine, with reduction of fluid intake having no effect on the concentration of the urine. There are several different types of DI, each with a different cause...
as opposed to other causes of polydipsia
Polydipsia
Polydipsia is a medical symptom in which the patient displays excessive thirst. The word derives from the Greek πολυδιψία, which is derived from πολύς + δίψα...
(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
Vasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
) during this test is also necessary.
If there is no change in the water loss despite fluid deprivation, desmopressin
Desmopressin
Desmopressin is a synthetic replacement for vasopressin, the hormone that reduces urine production. It may be taken nasally, intravenously, or as a tablet...
may be administered to distinguish between the two types of diabetes insipidus
Diabetes insipidus
Diabetes insipidus is a condition characterized by excessive thirst and excretion of large amounts of severely diluted urine, with reduction of fluid intake having no effect on the concentration of the urine. There are several different types of DI, each with a different cause...
which are central & nephrogenic diabetes insipidus.
The time of deprivation may vary from 4 to 18 hours.
The serum osmolality and urine osmolality are both measured in the test.
Interpretation
The conditions can be distinguished in the following way:| Condition | Urine osmolarity in mOsm/kg, after fluid deprivation | After desmopressin Desmopressin Desmopressin is a synthetic replacement for vasopressin, the hormone that reduces urine production. It may be taken nasally, intravenously, or as a tablet... or vasopressin Vasopressin Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's... |
|---|---|---|
| excessive intake of fluid (primary polydipsia) | > 800 | > 800 |
| a defect in ADH Vasopressin Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's... production (central/neurogenic diabetes insipidus Neurogenic diabetes insipidus Neurogenic diabetes insipidus, more commonly known as central diabetes insipidus, is due to a lack of vasopressin production in the brain... ) |
< 300 | > 800 |
| a defect in the kidneys' response to ADH Vasopressin Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's... production (nephrogenic diabetes insipidus Nephrogenic diabetes insipidus Nephrogenic diabetes insipidus is a form of diabetes insipidus due primarily to pathology of the kidney. This is in contrast to central/neurogenic diabetes insipidus, which is caused by insufficient levels of antidiuretic hormone /Argenine Vasopressin... ) |
< 300 | < 300 |