Monitoring of proteinuria in phase I studies in healthy male subjects

The quantitative measurement of urinary marker proteins may improve the sensitivity of monitoring renal function in healthy male subjects in phase I studies. Little is known about the variability of physiological proteinuria in young, healthy male subjects. Thus, the biological and analytical variability of three marker proteins, i.e. albumin, alpha(1)-microglobulin and N-acetyl-beta-D-glucosaminidase (NAG), were investigated in this population.

Seven young, healthy male subjects participated in a prospective two-way cross-over study, and 139 in a retrospective study. Albumin and alpha(1)-microglobulin were determined by immunological methods (radial immunodiffusion and/or kinetic nephelometry), and NAG by enzyme activity in a colorimetric assay.

The inter-assay precision of NAG, albumin and alpha(1)-microglobulin is good (< 15%) if automated kinetic nephelometry is applied for albumin and alpha(1)-microglobulin determination, but less impressive (< 25%) with radial immunodiffusion. The highest frequency of detectable proteinuria and highest creatinine-adjusted protein levels are found in the second morning urine voided after a night's rest. The intra-individual biological variability of NAG excretion from day to day is low (CV: 15-25%), irrespective of outpatient or inpatient settings. By contrast, albumin and alpha(1)-microglobulin excretion can differ by a factor of 2-3 from day to day, and higher levels are predominantly found in outpatient settings. The reference ranges for young, healthy male subjects are generally lower than published in cross-sectional studies in the total healthy population.

These findings and established reference ranges for young, healthy male subjects may assist in the evaluation of proteinuria in clinical pharmacological phase I trials.