Dr.Padmesh. V INVESTIGATIONS: Contd… High Plasma Osmolality <300 mOsm/kg WATER DEPRIVATION TEST Serum Osmolality >270
Dr.Padmesh. V WATER DEPRIVATION TEST-Determines ability of kidneys to concentrate urine.-Useful in the diagnosis of DI.-Requires careful supervision because dehydration and hypernatremia may occur.
Dr.Padmesh. VWATER DEPRIVATION TEST : Method: Begin the test after a 24-hr period of adequate hydration & stable weight. Obtain a baseline weight after bladder emptying. Restrict fluids for 7 hours. Measure body weight and urine specific gravity and volume hourly. Check serum Na+ and urine and serum osmolality every 2 hr. Terminate the test if weight loss approaches 5%.
Dr.Padmesh. VWATER DEPRIVATION TEST: Interpretation: Normal individuals & Psychogenic DI: Central or Nephrogenic DI: When water is deprivedWill concentrate urine (to 500-1400 mOsm/L) Urine osmolality remains <150-300 mOsm/LPlasma osmolality will be 288-291 mOsm Plasma Osmolality > 300 mOsmUrine specific gravity rises to at least 1.010 Urine Specific gravity remains <1.005 Urine volume decreases significantly No significant reduction of urine volumeThere will be no appreciable weight loss. Weight loss of up to 5% usually occurs
Dr.Padmesh. V VASOPRESSIN RESPONSE TEST:To differentiate CENTRAL D.I from NEPHROGENIC D.I Baseline Urine osmolality is recorded Vasopressin injection given Urine Osmolality measured at 1 hr & 4 hrs after injection Increase in urine osmolality>50% increase from baseline <50% increase from baseline CENTRAL D.I NEPHROGENIC D.I
Dr.Padmesh. V OTHER TESTS: Central D.I: MRI of hypothalamic-pituitary region Nephrogenic D.I: Renal imaging Genetic Studies as required.