Background: Patients with type 1 diabetes mellitus and microalbuminuria often have elevated blood pressure while they are asleep, but it is not known whether the elevation develops concomitantly with microal-buminuria or precedes it. Methods We monitored 75 adolescents and young adults who had had type 1 diabetes with normal urinary albumin excretion and blood pressure for more than five years. Ambulatory blood-pressure monitoring was used to assess blood pressure at the initial evaluation and about two years later, at which time all subjects had normal urinary albumin excretion. Subsequently, subjects were monitored for the development of microalbuminuria. Results Microalbuminuria developed in 14 subjects, whereas the other 61 continued to have normal urinary albumin excretion. The mean (±SD) systolic pressure during sleep increased significantly in the subjects who ultimately had microalbuminuria (from 109.9±11.3 to 114.9±11.7 mm Hg, P=0.01) but not in the subjects with normal albumin excretion (from 106.0±8.8 to 106.4±14.8 mm Hg). The risk of progression to microalbuminuria was examined in relation to the ratio of systolic pressure during sleep to systolic pressure in the daytime. A ratio of 0.9 or lower, used to define a normal fall in nocturnal pressure, had a negative predictive value of 91 percent for the development of microalbuminuria. Moreover, the risk of microalbuminuria was 70 percent lower (95 percent confidence interval, 44 to 110 percent) in subjects with a ratio of 0.9 or less than in those with a ratio higher than 0.9 (P=0.01). Conclusions In persons with type 1 diabetes, an increase in systolic blood pressure during sleep precedes the development of microalbuminuria. In those whose blood pressure during sleep decreases normally, the progression from normal albumin excretion to microalbuminuria appears to be less likely.
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