24-h ambulatory blood pressure, daytime and nighttime urinary albumin and retinol-binding protein excretion in type I diabetic patients.

We studied 24-h ambulatory blood pressure (SBP, DBP), actual glycemic control assessed from seven blood glucose measurements, 16-h daytime and 8-h nighttime urinary excretion of albumin (UAE) and retinol-binding protein (URBP) in 20 normoalbuminuric (group A, nighttime UAE < 20 micrograms/min) and 20 microalbuminuric and low-proteinuric type I diabetic patients (group B, nighttime UAE 20-500 micrograms/min) matched for age and diabetes duration. Glycemic control was similar in the two groups. Daytime and nighttime SBP and DBP were higher in group B compared to group A (p < 0.01). Nighttime decrease in SBP and DBP correlated with nighttime decrease in UAE in group B (p < 0.05, p < 0.001), but not in group A. There was no correlation between BP and actual glycemic control in either group. We found higher daytime and nighttime URBP in group B compared to group A (p < 0.05). We conclude that, in microalbuminuric and low-proteinuric patients, daytime and nighttime BP was elevated but still in the normal or borderline range, and nighttime decrease in BP correlated with nighttime decrease in UAE but not with actual glycemic control. Increased URBP in these patients suggests slightly impaired proximal tubular function in early stages of diabetic nephropathy.