• We simplified the procedure for identifying children with diabetes insipidus by using the relationship between urine and plasma osmolality (Uosm and Posm). We defined the normal Uosm-Posm relationship as the area within the 95% confidence regions for pairs of osmolality measurements obtained from normal children during periods of free access to fluids and after oral hydration. In 13 patients with diabetes insipidus, Uosm-Posm coordinates were outside these regions in 50 of 64 pairs (one to ten per patient) during periods of free access to fluids. After three hours of fluid deprivation, the Uosm-Posm relationship was abnormal in 12 patients; the 13th was unable to void. For those with a normal Posm, and Uosm less than Posm, another pair of osmolality measurements after three hours of fluid restriction should determine the diagnosis.
(Am J Dis Child 1981;135:839-841)