<prompt> Which of the following statements about Diabetes Insipidus is true:Urine osmolality should be 300 mosmLPlasma osmolality should be 280 mmolLWater deprivation test is requiredPlasma osmolality should be 300 mosmL prior to H2O Deprivation  <response>: Answer is C Water deprivation test is required : Diagnosis of diabetes insipidus often requires a water deprivation test. Water deprivation test is used to establish the diagnosis of diabetes insipidus and to differentiate Central and Nephrogenic forms of Diabetes Insipidus. Patients with diabetes insipidus have a normal or increased plasma osmolality 280 mosml and decreased urine osmolality 300mosm1. Water deprivation test typically demonstrates an increase in plasma osmolality with failure of urinary osmolality to increase no change during H20 deprivation in cases of diabetes insipidus thereby suggesting the diagnosis. Diabetes Insipidus is associated with plasma osmolality 280 mosmkg and urinary osmolalitv 300 mosm kg In normal subjects the plasma osmolality ranges from 275-295 mosm kg while the range of urine osmolality is wide, from 40 to 1000 mosmkg depending on the state of hydration. After water deprivation the urine osmolality will normally rise to exceed 800 mosmkg while the plasma osmolality remains below 295 mosmkg UP 2 In Diabetes Insipidus subjects the plasma osmolality ranges from normal to high 275 mosmkg while the urine osmolality is typically 300 mosm1. After water deprivation plasma osmolality rises to 295 mosmkg while urinary osmolality fails to rise appropriately Fails to rise to 300 mosmkg UP Ratio 2.0 Water deprivation test is often required to establish a diagnosis of Diabetes insipidus Water deprivation test is indicated in patients with hypotonic polyuria Uosm 300 mosmkg and a plasma osmolality 410 within the normal range Posm 275 -- 295 mosmkg to establish the diagnosis of diabetes insipidus and differentiate central nephrogenic forms. 