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WATER DEPRIVATION TEST

NO WATER 2-3 HRS PRIOR TO TEST

MEASURE URINE VOLUME AND OSMOLALITY EVERY HOUR

MEASURE SERUM SODIUM AND OSMOLALITY EVERY 2 HRS

URINE OSM >600mOsm/kg

PRIMARY POLYDIPSIA

YES

U.OSM STABLE ON 2-3 HRLY MEASUREMENTS

PLASMA OSMOLALITY>295mOsm/kg or plasma Na >145 mOsm/kg

NO

ADMINISTER DESMOPRESSIN

MONITOR URINE OSM AND VOLUME EVERY 30 MINS FOR 2 HRS

YES

CONTINUE TESTING UNTIL ABOVE TEST POINT IS REACHED

NO

CENTRAL DI: HIGH U. OSM

NEPHROGENIC DI: SMALL/ NO INCREASE IN U. OSM