Background: The cytokine osteopontin is involved in the pathophysiology of experimental acute kidney injury. We have tested the hypothesis that osteopontin levels might serve as a biomarker predicting outcome in critically ill patients requiring renal replacement therapy after acute kidney injury.
Methods: We measured circulating plasma osteopontin levels in 109 critically ill patients with acute kidney injury at inception of renal replacement therapy and 4 weeks thereafter. Critically ill patients without acute kidney injury served as controls. Osteopontin was measured with ELISA.
Results: Baseline osteopontin levels in patients with acute kidney injury were significantly higher compared with controls (P<0.0001). Baseline osteopontin levels in patients recovering from acute kidney injury were significantly elevated compared with patients with permanent loss of kidney function after acute kidney injury (P=0.01). In addition, in patients recovering from acute kidney injury without further need for renal replacement therapy, osteopontin levels were significantly lower 4 weeks after initiation of renal replacement therapy (P=0.0005). Moreover, multivariate Cox analysis revealed osteopontin levels at renal replacement therapy inception as an independent and powerful predictor of mortality (P<0.0001). In the ROC-curve analysis, an osteopontin cut-off value of 577 ng/mL separated survivors from non-survivors with a sensitivity of 100% and a specificity of 61% (AUC 0.82; 95% confidence interval: 0.74-0.89; P<0.0001).
Conclusions: Osteopontin may serve as a novel biomarker for both, overall survival and renal outcome in critically ill patients with acute kidney injury, that require renal replacement therapy.