Diagnostic utility of plasma and urine KIM-1 levels in clear cell renal cell carcinoma: an observational prospective study

Kidney injury molecule-1 (KIM-1) is a transmembrane glycoprotein expressed in injured proximal tubules and renal cell carcinoma (RCC). This study evaluated urinary (uKIM-1) and plasma (pKIM-1) concentrations in patients with clear cell RCC (ccRCC) as potential diagnostic and prognostic biomarkers. A prospective observational study included 73 patients undergoing nephrectomy for renal tumors and 34 healthy volunteers. KIM-1 levels were measured using ELISA and analyzed in relation to tumor size, TNM stage, WHO/ISUP grade, and histopathological features. Diagnostic performance was assessed using ROC curves. Correlations were evaluated using Spearman coefficients. Both uKIM-1 and pKIM-1 levels were significantly higher in ccRCC patients compared to those with non-ccRCC tumors and healthy individuals ( p < 0.001). pKIM-1 > 75 pg/ml demonstrated high diagnostic performance for ccRCC (AUC = 0.93, sensitivity = 90.4%, specificity = 94.1%). uKIM-1 > 1.15 ng/mg uCr showed lower performance (AUC = 0.78, sensitivity = 69%, specificity = 73.5%). Biomarker levels correlated positively with tumor size ( R = 0.66), TNM stage ( R = 0.61), and histological grade ( R = 0.58). Both markers were elevated in tumors with necrosis and perirenal fat invasion. KIM-1 is a promising non-invasive biomarker for ccRCC. Plasma KIM-1 > 75 pg/ml distinguishes ccRCC from healthy individuals with high sensitivity and specificity, while also correlating with tumor aggressiveness. Its measurement may support diagnosis, risk stratification, and follow-up in ccRCC patients.