Circadian rhythm of albumin excretion rate in healthy subjects.

Many studies have reported the predictive role of unphysiological levels of microalbuminuria for the development of diabetic nephropathy. It is known that physiological levels of 24-h microalbuminuria do not exceed 20 micrograms/min (28.8 mg/day), but a few data are available for shorter periods. Since an accurate 24-h urine collection is difficult to obtain in screening programs, it seems important to study whether a circadian oscillation exists and, if so, to find more precise reference values. Eleven healthy subjects (mean age 30.6 +/- 2.46 years) with normal glucose tolerance and no family history of diabetes mellitus or nephropathy were studied during the usual routine activity. Urines were collected 6 times at 4-h intervals. It was possible to document the existence of a statistically significant circadian rhythm with the following parameters: MESOR 6.95 +/- 0.49 micrograms/min; amplitude 1.96 +/- 0.37 micrograms/min; acrophase 15(06); 95% CL 13(01)-17(45). These data show that reference values are higher during daytime as compared with nighttime and suggest that the time of urine collection must be taken into consideration in order to define the upper physiological limits more precisely.