Urinary Cells Flow Cytometry in Renal Disease: A Systematic Review of Diagnostic and Prognostic Applications

Background: Urinary cellular biomarkers detected by flow cytometry have emerged as promising non-invasive tools for the diagnosis, prognosis, and monitoring of renal and urological diseases. However, a comprehensive synthesis of their clinical applicability is lacking. Objectives: This review aimed to systematically evaluate and summarize the evidence of urinary cellular biomarkers identified through flow cytometry in human populations with renal or urological diseases. Methods: A systematic search of PubMed, Scopus and Web of Science was conducted from inception to January 2025. Observational studies analyzing urinary samples by flow cytometry were included, whereas animal studies, genetic-only analyses and studies with incomplete data were excluded. Data extraction and risk of bias assessment were performed independently by two reviewers using a standardized form and the Newcastle-Ottawa Scale. Due to heterogeneity in study populations, designs, and cytometry methods, results were synthesized narratively. Results: Of 3938 records screened, 23 studies met the inclusion criteria. All studies applied flow cytometry to characterize urinary cellular biomarkers across renal diseases. Several studies reported promising diagnostic and monitoring applications, but substantial heterogeneity in study design, cytometry protocols, and marker panels limited comparability. Longitudinal analyses and robust prognostic validation were infrequently reported. Conclusions: Urinary cellular biomarkers assessed by flow cytometry represent a promising non-invasive approach for evaluating renal and urological diseases. However, clinical implementation remains constrained by heterogeneity and insufficient validation. Future research should focus on standardized methodologies and large prospective studies to establish their diagnostic and prognostic utility.