We have recently identified a new clinical syndrome in patients receiving warfarin for anticoagulation therapy. This syndrome has been named warfarin-related nephropathy (WRN), and patients with chronic kidney disease (CKD) appear to be particularly susceptible. WRN is defined as an acute increase in international normalized ratio (INR) to > 3.0, followed by evidence of acute kidney injury (AKI) within 1 week of the INR increase. AKI was defined as a sustained increase in serum creatinine of greater than or equal to 0.3 mg/dL. The AKI cannot be explained by any other factors, and the kidney biopsy demonstrates extensive glomerular hemorrhage with tubular obstruction by red blood cells (RBCs). Beyond AKI, WRN is a significant risk factor for mortality within the first 2 months of diagnosis and it accelerates the progression of CKD. We demonstrated that 5/6 nephrectomy in rats is a suitable experimental model to study WRN. Animals treated with warfarin showed an increase in serum creatinine and morphologic findings in the kidney similar to those in humans with WRN. Our recent evidence suggests that novel oral anticoagulants may induce AKI. Diagnosis of WRN may be challenging for a renal pathologist. A few cases with suspected WRN and pathologic considerations are described.
Acute Kidney Injury* ; Animals ; Anticoagulants* ; Biopsy ; Creatinine ; Diagnosis ; Erythrocytes ; Hemorrhage ; Humans ; International Normalized Ratio ; Kidney ; Models, Theoretical ; Mortality ; Nephrectomy ; Pathology* ; Rats ; Renal Insufficiency, Chronic ; Risk Factors ; Warfarin

Anticoagulant-related nephropathy (ARN) was initially described in patients on warfarin (as warfarin-related nephropathy) and recently in those using dabigatran. Herein, we report clinical history and kidney biopsy findings in a patient on apixaban (Eliquis). Initiation of treatment with apixaban resulted in aggravation of preexisting mild acute kidney injury (AKI). A few days after apixaban therapy, the patient became oligoanuric, and kidney biopsy showed severe acute tubular necrosis with numerous occlusive red blood cell casts. Only one out of 68 glomeruli with open capillary loops had small segmental cellular crescent. Therefore, there was major discrepancy between the degree of glomerular injury and the glomerular hematuria. Considering that the onset of this AKI was associated with apixaban treatment initiation, we propose that this patient had ARN associated with factor Xa inhibitor (apixaban), which has not previously been described. Monitoring of kidney function is recommended after initiation of anticoagulant therapy.
Acute Kidney Injury* ; Biopsy ; Capillaries ; Dabigatran ; Erythrocytes ; Factor Xa ; Hematuria ; Humans ; Kidney ; Necrosis ; Warfarin