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.
Bibliographical noteFunding Information:
Dr. Wagner's conflict of interest statement is as follows: Dr. Wagner has no conflicts of interest to disclose. Dr. Accurso's conflict of interest statement is as follows: Dr. Accurso has received grant support from the National Institutes of Health and the Cystic Fibrosis Foundation. He has served as a consultant to Inspire Pharmaceuticals, Inc. in the last three years. He has participated in industry studies through the Cystic Fibrosis Foundation Therapeutic Development Network (Gilead Sciences, Inc.; Targeted Genetics, Inc.; PTC Therapeutics, Inc.; Vertex Pharmaceuticals, Inc.; Altus Biologics, Inc.; Digestive Care, Inc.; KalobBios Pharmaceuticals, Inc.). Dr. Laguna's conflict of interest statement is as follows: Dr. Laguna has received grant support from the American Thoracic Society and the Cystic Fibrosis Foundation. She has provided an educational symposium sponsored by Hill-Rom.
This work was supported by the Cystic Fibrosis Foundation ( CFF LAGUNA06A0 ) and the National Institutes of Health ( NIH 1UO1HL081335-01 , UL1 RR025780 and M01RR00069 ). The authors did not receive writing assistance for this manuscript. The study sponsors did not have any role in the study design; in the collection, analysis and interpretation of the data; in the writing of the manuscript; and in the decision to submit the manuscript for publication.
- Cystic fibrosis
- Normalization factor
- Pulmonary exacerbation
- Specific gravity
- Urinary biomarkers
- Urinary creatinine