title: Validity of protein-osmolality versus protein-creatinine ratios in the estimation of quantitative proteinuria from random samples of urine in children.
abstract: BACKGROUND
  Proteinuria is an important marker of kidney disease. Simple methods to determine the presence of proteinuria in a semiquantitative fashion require measurement of either a protein-creatinine or protein-osmolality ratio.
  
  
  METHODS
  Urine samples from 134 healthy infants and children and 150 children from the pediatric nephrology practice were analyzed to develop normative data for protein-osmolality ratios on random urine samples and compare protein-osmolality with protein-creatinine ratio as a predictor of 24-hour urine protein excretion. Children were grouped according to age. Three groups were established: infants (<2 years), younger children (2 to 8 years), and older children (9 to 18 years). An adult cohort was similarly analyzed.
  
  
  RESULTS
  For healthy children older than 2 years, the optimal value discriminating normal from abnormal protein excretion was determined to be a protein-osmolality ratio of 0.15 mg x kg H2O/mOsm. L; for children between 2 and 8 years old, 0.14; and for children older than 8 years, 0.17 (P = not significant between age groups). The corresponding optimal cutoff value for protein-creatinine ratio for the entire group of children older than 2 years is 0.20. Area under the curve analysis of receiver operator characteristic curves showed protein-creatinine ratio was superior to protein-osmolality ratio for predicting abnormal amounts of proteinuria in children and adolescents (P < 0.0001). In adults, both ratios are equally accurate.
  
  
  CONCLUSIONS
  Given the superiority of protein-creatinine ratio in children, it would be appropriate to screen urine samples for proteinuria using protein-creatinine ratio rather than protein-osmolality ratio.
authors.affiliation: Division of Pediatric Nephrology, Mayo Clinic, Rochester, MN 55905, USA. bmorgenstern@mayo.edu
authors.forename: Bruce Z
authors.initials: BZ
authors.lastname: Morgenstern
authors.forename: Lavjay
authors.initials: L
authors.lastname: Butani
authors.forename: Peter
authors.initials: P
authors.lastname: Wollan
authors.forename: David M
authors.initials: DM
authors.lastname: Wilson
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Larson
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D007223:Infant; D007674:Kidney Diseases / Q000175:diagnosis / Q000652:urine; D008297:Male; D008403:Mass Screening; D009994:Osmolar Concentration; D011507:Proteinuria / Q000652:urine*; D012372:ROC Curve; D016482:Urinalysis / Q000379:methods*
chemical_list: D003404:Creatinine