Validity of protein-osmolality versus protein-creatinine ratios in the estimation of quantitative proteinuria from random samples of urine in children.
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.
Morgenstern
Bruce Z
BZ
Division of Pediatric Nephrology, Mayo Clinic, Rochester, MN 55905, USA. bmorgenstern@mayo.edu
Butani
Lavjay
L
Wollan
Peter
P
Wilson
David M
DM
Larson
Timothy S
TS
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*
D003404:Creatinine