The applicability of urinary creatinine as a method of specimen normalization in the cystic fibrosis population

Background: Urine specimens are commonly used in biomarker research. Urinary creatinine (UCr) is often used to adjust for urine analyte concentration. We aim to explore the applicability of UCr as a normalization method in a cystic fibrosis (CF) population during hospitalization. Methods: Multiple spot urine samples were collected from CF patients hospitalized for a pulmonary exacerbation. Single spot specimens were obtained from asthmatics and healthy children for comparison. The assumptions and implications from the use of UCr as a normalization factor for urinary desmosine measurements were investigated. Results: UCr differed significantly across disease groups and decreased significantly over time in the CF population. Differing results were obtained when contrasting normalization by UCr with specific gravity. Conclusions: UCr levels are not completely attributable to simply variations in urine concentration. Analysis of urinary biomarker measurements should be initiated with an understanding of the relative effects of the normalization process on the results. (C) 2010 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.