Water deprivation test

Following a water-deprivation test, Irene s urine was found to have an osmotic pressure of 460 mOsm kg-1 water. The normal kidney can concentrate urine to approximately 1000 mOsm kg-1 water. A diagnosis of diabetes insipidus was made. 

Water deprivation and exogenous ADH administration are two diagnostic tests that can be used to differentiate neurogenic from nephrogenic DI. The latter test is pursued only after there is a failure to produce concentrated urine in response to the water-deprivation test (Schott 1998). Until recently, the most commonly used form of exogenous ADH was a water-insoluble tannate of arginine vasopressin extracted from the posterior pituitary and suspended in peanut oil. This preparation is no longer available. Currently,... 

Document polyuria (urine volume >2.5L/day) and exclude glycosuria. If desired, creatinine excretion can be measured as an estimate of completeness of urine collections snbstances that inflnence ADH secretion should be avoided (e.g., nicotine, alcohol, and caffeine). If plasma osmolality is >295 mOsm/kg or if serum sodium concentration >145mmol/L, primary polydipsia is unlikely proceed with the overnight water deprivation test (Box 50-9) or the hypertonic saline infusion test (Box 50-10). 

Overnight water deprivation test (Box 50-9) If the ratio of urine to plasma osmolality is <1.5 at the end of the test, primary polydipsia is unlikeiy. Measure plasma and urine osmolalities and plasma ADH concentrations at the end of the test use these relationships to differentiate normal, nephrogenic, or hypothalamic diabetes insipidus, and psychogenic polydipsia. If urine osmoiahty is <400 mOsm/kg at the end of the test, give 5 U of aqueous vasopressin subcutaneously. If urine osmolality increases >10%, hypothalamic diabetes insipidus is probable if urine osmolality does not increase, nephrogenic diabetes insipidus is highly probable. 

FIGURE 49-5. Water deprivation test The change in plasma osmolality is plotted against the change in urine osmolality following water deprivation and subcutaneous administration of 5 meg of desmopressin acetate. DI, diabetes insipidus Posm, plasma osmolality Uosm, urine osmolality. (Adapted from Rose et al. )... 

The causes of polyuria are summarized in Table I. Occasionally it may be necessary to deprive a patient of water in an effort to find the cause of excessive polyuria. The water deprivation test involves complete lluid deprivation during a 24-hour period, with measurement of the osmolality of all the urine specimens passed during the. second 12 hours of the test. An osmolality... 

Water deprivation test poiyuria persists urine does not concentrate... 

Measurement of the renal concentrating ability by the water deprivation test. 

WATER DEPRIVATION TEST (URINE CONCENTRATION TEST) 375 Disturbances of water balance... 

Evaluation of urine concentrating ability. Urine concentrating ability is determined using the water deprivation test or the exogenous vasopressin test. 

In this category of models the animal learns a performance, typically to abstain from a behavior that it would normally display according to its natural and current tendency. For example, in the so-called Vogel test a partly water-deprived and thirsty rat learns that, during a signaled period, every lick at the water spout will be followed by a mild electric foot-shock. This sequence induces anxiety and an untreated (control) animal will abstain from drinking. However, animals pretreated with anxiolytic drugs will overcome their inhibition and tolerate at least some of the shocks and drink even when punished. 

Armstrong si. (239) used a test that required water-deprived rats to press four levers In a preset sequence to obtain water. After administration of EA 3443 by an unstated route, the ED50 for a minimal mydriatic effect was 37 >ig/kg that for reduction of the number of drops of water obtained within a given period was 53.2 >ig/kg. 

In practice, the water deprivation te.st is extremely unpleasant for the patient. It is potentially dangerous if there is severe inability to retain water. The test must be terminated if weight loss exceeds 3 kg or if more than 3 litres of urine is passed. 

Drinking tests are feasible when testing older subjects. Nolte and Mason (1995) used a single-choice drinking test to assess pup response to trigeminal irritants they were exposed to in utero. First, pups were adapted to an 18-h water deprivation schedule. Pups were presented with tap water in a 10 ml graduated sipper... 

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