A standardized desmopressin test of renal concentrating ability

Renal concentration tests were carried out on 45 healthy volunteers and 106 patients with chronic renal disease of moderate degree involving impaired concentrating ability. Each subject served as his own control. The control experiment involved a total of 36 hr of "dehydration" (no fluids per os or food with a high fluid content such as fruit) in which 4 hr clearance periods were started from the 12th and continued to thd 36th hr. The first 12 hr involved an overnight period from 20.00 hr. One week later the same subjects were given 10 micrograms demopressin (dDAVP) at the 13th hr and a subsequent 4 hr clearance period provided blood and urine samples to compare desmopressin-induced urine concentration with various stages of concentration during oral fluid withdrawal alone. The drug was given intranasally. We measured urine osmolality and concentrations of urea. Na, K and calculated the U/P creatinine concentration ratios and creatinine clearances (CCr). Using Uosm as the criterion, the dDAVP experiment at 12 hr gave the same results as 24 hr of fluid withdrawal alone. With the U/PCr ratio as the criterion, dDAVP + 12 hr gave the same results as 36 hr of fluid withdrawal alone. Between 32 and 36 hr dehydration, CCr decreased - otherwise it remained unchanged in both healthy and ill subjects, with and without dDAVP. The only side-effect was the discomfort of more than 12 hr dehydration. This would appear to simplify a potentially useful diagnostic and prognostic test.