Night-time polyuria and urine hypo-osmolality in enuretics identified by nocturnal sequential urine sampling--do they represent a subset of relative ADH-deficient subjects?

Early morning urine osmolality was tested in two urinary specimens, one taken immediately upon awakening and the other approximately 30 min thereafter, in 52 enuretic and 15 non-enuretic children. In a follow-up study, using the same study population, urine osmolality and volume were measured sequentially at 3-h intervals at 19.00, 22.00, 01.00, 04.00 and 07.00 h. Thereafter, all enuretics were treated by intranasal DDAVP for a 6-month period. There were no differences in urinary osmolality between enuretic and non-enuretic children when comparing the two early morning specimens. Nor were there any differences between groups in urine osmolalities at 19.00, 01.00 and 07.00 h. In contrast, at 04.00 h, urine osmolality was significantly lower in 17 of 52 enuretics [designated as ADH-negative (ADH-)] compared to the remaining enuretics [designated as ADH-positive (ADH+)] and non-enuretic children (610 +/- 251 vs 995 +/- 195 and 1089 +/- 195 mosmol/kg H2O, respectively, p < 0.05). This decreased osmolality was paralleled by an increase in urine production during the time period 01.00-04.00 (83 +/- 24 vs 52 +/- 18 and 45 +/- 22 ml, respectively, p < 0.05). At the end of the 6-month period of DDAVP treatment, the percentage response was similar between the ADH- and ADH+ enuretics (79% vs 75%). However, the time taken to achieve a response was quicker in the ADH- subjects. These data suggest the existence of a subgroup of enuretics whose underlying pathophysiology is the development of nocturnal polyuria probably due to a relative night-time ADH deficiency. Nocturnal sequential monitoring of urinary osmolality, as described above, allows identification of this subgroup.