Urinary nerve growth factor: a biomarker of detrusor overactivity? A systematic review

Nerve growth factor (NGF) is a signalling protein that interacts with specific receptors in autocrine, paracrine and endocrine modes. It is produced by bladder smooth muscle and urothelium. Patients with overactive bladder and detrusor overactivity (DO) have been found to have increased urinary NGF levels in several small studies. The objective of the review was to assess the accuracy of NGF as a biomarker in the diagnosis of DO by a systematic review of the literature. A systematic search of MEDLINE, Embase, CINAHL, MEDION and LILACS databases was conducted (inception till December 2012). Selection criteria included studies where NGF (as a biomarker for DO) and urodynamics were performed in humans with symptoms of overactive bladder. Two reviewers independently selected articles and extracted data on study characteristics, quality and results. All the eight included studies were of case-control design. A meta-analysis was not performed as there were variations in the quality, methods of performing the NGF assay, different NGF cut-offs used and the format of reporting findings. Two studies used a cut-off of 0.05 for NGF levels. Six studies observed a trend towards higher NGF levels in patients with DO. There was a trend towards higher NGF in patients with DO. However, the data are imprecise and hence cannot be recommended for use in current clinical practice.