Urinary brain-derived neurotrophic factor and nerve growth factor as noninvasive biomarkers of overactive bladder in children.

"Potential conflict of interest: None declared."

"This study was funded by Croatian Science Foundation (grant UIP-2017-05-5379). The funding source had no role in the design, practice, or analysis of this study. A limitation of this study was that neurotrophin concentrations were analysed at different time intervals after sample collection. To our knowledge, there are no studies on the stability of neurotrophins in urine samples stored at - 80 °C. It was unfeasible to standardise the interval from collection to analysis because this was a prospective intervention study in the paediatric population and the target proteins were analysed with immunoassays performed on batches of 80 samples. A second limitation was that the patient and control groups were not matched for age and sex. The reason for this limitation was that this study was performed as part of a larger study funded by the Croatian Science Foundation, in which one of the objectives was to determine the age and sex variations of neurotrophins in healthy children. Therefore, it was not possible to have a disproportionate number of girls in the control group as in the patient group."

"The protocol for the research project was approved by the Institutional Ethics Committee (Approval No. 02-26/10-8-1), and it conforms to the provisions of the Declaration of Helsinki. Informed consent was obtained from the participants and their legal guardians before the study procedures. The study was registered at ClinicalTrials.gov under NCT02704013 (ID: pOAB-CHZ-01)."