Water deprivation test
Used to dx DI Withhold fluids and measure urine osmolality every hour When urine osm is stable (<30 mOsm/kg hourly increase for 3hrs) inject 2g desmopressin subcutaneously. Measure urine osm 1 hour later Normal patients will have an increase in urine osm with dehydration and no response to ADH Patients with DI will have no increase in urine osm ut a response to ADH Patients with nephrogenic DI will have no increase with dehydration or ADH