Abstract
BACKGROUND: Urine red blood cell distribution (URD), defined as the percentage of small RBC fractions measured by the Sysmex UF-5000 analyzer, demonstrates diagnostic accuracy comparable to dysmorphic RBC analysis for distinguishing glomerular from nonglomerular hematuria. To improve diagnostic performance, we developed the UPC index, integrating URD with urine protein strip and serum creatinine values. METHODS: We analyzed 813 patients from three tertiary centers in Korea between December 2022 and December 2023. Patients were classified into four diagnostic categories: glomerular diseases (GD, N = 285), renal diseases (RD, N = 286), extrarenal diseases (ERD, N = 197), and isolated hematuria (IH, N = 45). The RD group included acute kidney injury (AKI), chronic kidney disease (CKD), nephrotic syndrome (NS), and tubulointerstitial disease (TID). Data included urinalysis and renal function parameters. RESULTS: In distinguishing GD from ERD, the UPC index demonstrated the highest diagnostic performance, with an area under the curve (AUC) of 0.857. This outperformed other parameters, including URD (AUC = 0.779), albumin-creatinine ratio (ACR; 0.746), protein-creatinine ratio (PCR; 0.648), serum creatinine (0.555), and blood urea nitrogen (BUN; 0.528). Among patients with renal diseases, the UPC index showed a significant difference between the CKD, AKI, and NS groups compared to the TID group, whereas URD values did not show a significant difference between CKD and TID. At a cut-off value of 3.99, UPC achieved a sensitivity of 86.7% and specificity of 73.1% for identifying GD. CONCLUSION: UPC is a reliable and objective screening index suggestive of glomerular hematuria, with better performance than URD in a conservative reference framework.