Quantification of proteinuria in children using the urinary protein-osmolality ratio

A prospective study was conducted to determine the correlation of early morning urinary protein/osmolality ratio (mg/l/mosmol/kg) with 24-h urinary protein excretion (mg/m²/day). Study patients consisted of 53 children (aged 1 month to 15 years). Early morning urine samples and 24-h urine samples were collected and analyzed. In group 1 (children without proteinuria), early morning urinary protein/creatinine ratio (Uprot/Ucr, mg/mg) was 0.061±0.011 and the protein/osmolality ratio (Uprot/Uosm, mg/l/mosmol/kg) was 0.073±0.014. Twenty-four hour urinary protein excretion in group 1 had no significant correlation with Uprot/Ucr or Uprot/Uosm. In group II (children with proteinuria), Uprot/Ucr was 5.78±1.10 and Uprot/Uosm was 4.42±1.34. Twenty- four hour urinary protein excretion in group 2 was 1483.6±303.7 mg/m²/day and its correlation with both Uprot/Uosm and Uprot/Ucr was highly significant (r= 0.87, P<0.001 and r=0.88, P<0.001, respectively). The accepted nephrotic level of proteinuria of 40 mg/m²/h coincides with a Uprot/Uosm ratio of 1.9. In conclusion, early morning urinary Uprot/Uosm is a simple and potentially useful test for 24-h urinary protein excretion, and possibly could be used safely for the assessment of the degree of proteinuria in children. Received: 13 April 1999 / Revised: 23 February 2000 / Accepted: 15 August 2000