Urine as a source of biomarkers and biological knowledge in chronic kidney disease

Albuminuria and estimates of glomerular filtration rate remain the main diagnostic and monitoring metrics used in people with chronic kidney disease (CKD). Although these are both useful markers of kidney disease, they represent the consequence rather than the cause of CKD, can neither detect disease at its earliest stages nor determine its aetiology, and are often suboptimal in guiding therapeutic intervention. By contrast, nucleotide, protein, peptide and metabolite findings from urine can provide a wealth of information about kidney-tissue biology and pathological processes, thereby representing a source of potential biomarkers for early disease detection, prognostication and therapeutic guidance. Urinary biomarker research is currently dominated by studies of protein biomarkers that reflect tissue injury and repair, inflammation and fibrosis, and can be combined for use in multi-marker panels. Data on biomarkers for guiding therapy are scarce, underscoring the urgent need for more targeted studies, given the availability of several new therapies that are effective in attenuating CKD progression and improving patient outcomes. Consequently, although several (mainly protein) biomarkers with evidenced potential to improve disease management are currently available, their clinical implementation is limited by the paucity of clinical and health-economic impact data, especially data on the combined use of urinary biomarkers and the latest therapies available for people with CKD.