[A case of acute kidney injury during warfarin therapy]

The patient was an 82-year-old female. She had been treated with warfarin for atrial fibrillation that developed after a heart valve replacement operation. She was admitted because of a progressive loss of renal function together with persistent microscopic hematuria and proteinuria. Although the renal biopsy showed only focal mononuclear cell infiltration and mild mesangial expansion in the glomeruli, the occlusive red blood cell casts were remarkable in the tubules and were accompanied by inflammatory and edematous changes in the surrounding interstitial area. After the adjustment of an excessively extended prothrombin time, her renal function gradually improved in parallel with the marked decrease in the microhematuria. It was assumed that an acute kidney injury observed in this case was caused by the occlusive red blood cell casts as a result of abnormal hemorrhage in the glomeruli due to focal glomerulonephritis and a warfarin overdose. The present case, therefore, suggests that a warfarin overdose is a potential risk factor for acute kidney injury in the presence of coexisting glomerular injury.