Urinary albumin excretion in healthy adult subjects: reference values and some factors affecting their interpretation.

A conventional radioimmunoassay has been used to measure urinary albumin concentration in overnight, recumbent and daytime, ambulant samples from 127 healthy, normotensive volunteers (mean age 33.3 yr SD 12.4; 59 males, 68 females). Reference values were obtained for urine albumin concentration (mg/l), albumin/creatinine ratio (mg/mmol), and albumin excretion rate (microgram/min). The frequency distributions of these variables were positively skewed, but became Gaussian on logarithmic transformation of the data. Albumin excretion was significantly higher in daytime, ambulant samples than in overnight, recumbent samples (p less than 0.001). Surface area was not correlated with urine albumin concentration but it was negatively correlated with urine albumin/creatinine ratio (p less than 0.05) due to the association between surface area and creatinine excretion. Urine albumin concentration was negatively correlated with age, but this was due to a higher urine flow rate in older subjects. There was no significant association with sex or with mean arterial blood pressure in the normal range. Two repeated measurements showed that variability was high and comparable for urine albumin concentration, albumin/creatinine ratio and albumin excretion rate: it was not significantly less in overnight, recumbent than in day-time, ambulant samples.