Osteopontin (OPN), a cytokine, may be a useful biomarker for predicting outcomes in critically ill patients with acute kidney injury (AKI), researchers reported.

Johan M. Lorenzen, MD, of Hannover Medical School in Hannover, Germany, and collaborators measured circulating plasma OPN levels in 109 critically ill patients with AKI at inception of renal replacement therapy (RRT) and four weeks thereafter. Critically ill patients without AKI served as controls.

Baseline osteopontin levels in AKI patients were significantly higher compared with controls, according to findings published in Nephrology Dialysis Transplantation (2011;26:531-537). Baseline levels were significantly elevated compared with patients with permanent loss of kidney function after AKI. In patients recovering from AKI without further need for RRT, OPN levels were significantly lower four weeks after RRT initiation.

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After adjusting for multiple potential confounders, OPN levels at the start of RRT was a strong and independent predictor of mortality. An OPN cutoff value of 577 ng/mL separated survivors from non-survivors, with 100% sensitivity and 61% specificity, according to investigators.

OPN has been shown to be a mediator of severe inflammation in patients with systemic inflammatory response syndrome and sepsis, perhaps by altering the release of interleukin-6 (IL-6), the researchers noted.

“We speculate that the level of critical illness and inflammation is reflected by circulating levels of OPN,” the authors wrote. “OPN might serve as a marker and mediator of multi-organ dysfunction through the retention of inflammatory cells and the release of IL-6. Death ensues as a consequence of severe inflammation. These patients present with the highest levels of circulating OPN.”