Nerve growth factor (NGF): a potential urinary biomarker for overactive bladder syndrome (OAB)?

Objective To review the current literature on the use of urinary nerve growth factor (NGF) as a potential biomarker for overactive bladder syndrome (OAB). Method A comprehensive electronic literature search was conducted using the PubMed database to identify publications relating to urinary NGF. Results There are a growing number of publications that have measured urinary NGF levels in different types of bladder dysfunction. These range from OAB, bladder pain syndrome, idiopathic and neurogenic detrusor overactivity, bladder oversensitivity and bladder outflow obstruction. Urinary NGF levels do appear to be raised in these pathological states when compared with healthy control samples. In patients with OAB, these raised urinary NGF levels appear to also reduce after antimuscarinics and botulinum toxin A, which indicates a potential use in monitoring responses to treatment. However, raised levels are not limited to OAB, which questions its specificity. Urinary NGF measurements are performed with an enzyme-linked immunosorbent assay using polyclonal antibodies to NGF. The technique requires standardisation, and the different antibodies to NGF require validating. Also a definition of what is the 'normal' range of NGF in urine is still required before it can be used as a diagnostic and prognostic tool. Conclusions Whilst the evidence for an increased urinary NGF in OAB appears convincing, many questions about its validity remain including: specificity, sensitivity, cost- and time-effectiveness. Many criteria for what constitutes a biomarker still need to be evaluated and met before this molecule can be considered for this role.