Biomarkers in kidney fibrosis: are they useful?

With the escalating cost of monitoring and follow-up required in the care of patients with chronic kidney disease (CKD), biomarkers are increasingly being investigated for their utility in predicting patients most at risk of decline in renal function in order to rationalize and target care. Putative biomarkers have also emerged as treatment targets, with the potential to develop novel therapeutics. However, biomarker studies in CKD are largely derived from single-sample collections in observational or nested case-control studies that are suboptimal in study design, analyses, and end points relevant to confirm the utility of specific biomarkers. It has been demonstrated that biomarker expression may be modified by declining kidney function. Hence, their value in predicting future kidney dysfunction is limited. Therefore, understanding the nature, mechanism of action, and how specific biomarkers interact with the CKD disease process is a crucial step in defining the potential for biomarkers to predict outcome, or alternatively, develop as a therapeutic target. Unlike conventional risk factors that, albeit partly, enable us to distinguish an individual at risk of cardiovascular disease, biomarkers in patients with CKD may not be required to be modifiable either directly or indirectly in the disease process or by therapy. Reproducibility and prospective validation remain major challenges for the burgeoning number of purported biomarkers in patients with CKD. It is highly likely a combination of conventional and novel biomarkers will be needed to accurately predict the risk of end-stage kidney disease. This review will focus on recently identified biomarkers and their utility in predicting progressive kidney fibrosis.