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.

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