Protein Biomarkers of Kidney Injury and Dysfunction: Emerging Evidence on Non-Coding RNAs

Background: Kidney biomarkers address different clinical questions, and their accuracy depends on the population, sample, timing, and outcome. Objective: To organize selected evidence on protein biomarkers of kidney injury and dysfunction and examine emerging clinical evidence on non-coding RNAs (ncRNAs). Methods: This structured comparative narrative review used PubMed and Google Scholar, with searches through 19 September 2026, supplemented by targeted source verification and literature updating during revision in October 2026. Published estimates were summarized descriptively, no new meta-analysis was performed. Filtration assessment, AKI detection, persistence, disease activity, and RNA discovery or validation were considered separately. Results: Cystatin C and proenkephalin provide filtration-related information; KIM-1, NGAL, L-FABP, and NAG address tubular injury or associated outcomes. Urinary IL-18 and serum IL-8 have limited stand-alone diagnostic value in pediatric AKI. [TIMP-2]×[IGFBP7] reflects cellular stress and near-term AKI risk. CCL14 concerns persistent AKI. uDKK3, VCAM-1, and serum cathepsin S have evidence specific to their applications. Urinary HBP and plasma 8-isoprostane describe complementary infection and oxidative-stress contexts. More recent syntheses revise previously reported estimates for KIM-1 and NGAL. Selected ncRNA studies show promising discrimination, but their populations, clinical contrasts, and validation stages differ. Conclusions: Organizing biomarkers by clinical question connects their biological information with distinct diagnostic and prognostic applications. Protein–ncRNA combinations offer a direction for prospective research, with clinical adoption requiring independent validation and added value beyond conventional assessment.