Recommendations for Pre-Analytical Urine Sample Handling To Allow Optimal Assessment of Albuminuria and Proteinuria A consensus report of the USA NKF Albuminuria – Proteinuria Workshop

Abstract Albuminuria and proteinuria are key biomarkers for diagnosing, staging, and monitoring of chronic kidney disease. Both are also strongly associated with renal and cardiovascular risk. Given their important diagnostic role, reliable measurement of urinary albumin and protein is essential for clinical practice and trials. However, variability in the methodology presently used to collect, store and prepare urine samples may influence assay performance and contribute to inconsistent results. In response to a call for harmonization, the United States of America National Kidney Foundation organized a workshop in April 2025 to define optimal methods and practices for measuring albuminuria and proteinuria. As part of this initiative, the available evidence on pre-analytical factors affecting urinary albumin and protein measurements was discussed. For this purpose, a narrative literature review was conducted to identify relevant studies focusing on urine collection strategies, including 24-hour versus single-void samples, timing of sample collection, the need for repeated measurements, clinical conditions that may cause false-positive results, and the effects of sample storage and handling under various temperature conditions. Given heterogeneity in study designs and outcome measures, findings were synthesized qualitatively. This consensus report summarizes the findings of this literature review and the resulting discussion. It highlights the importance of standardized urine collection and handling procedures to minimize biological and analytical variability. In addition, it provides practical recommendations.