Supratherapeutic International Normalized Ratio causing Nephropathy: A Rare Adverse Effect of Warfarin

There are many common causes of nephropathy (abnormal pathology of kidneys) such as diabetes, hypertension, autoimmune, and drugs. Amongst the drugs, warfarin has recently been recognized to cause nephropathy in rare cases. Warfarin-related nephropathy (WRN) is clinically defined as an increase in serum creatinine of 0.3 mg/dl within one week of international normalized ratio (INR) being greater than 3. A 61-year-old male was referred by his primary care physician (PCP) for having complaints of elevated creatinine associated with hematuria for one month. On evaluation with computed tomography (CT) of the abdomen/pelvis, it was revealed that he had small non-obstructing stones. The creatinine had increased from a baseline of 2.03 mg/dl to 6.8 mg/dl. Hemoglobin (Hb) had decreased from a baseline of 12.8 gm/dl to 8.1 gm/dl, the INR was 3.52. On subsequent days, the patient's renal function did not improve with fluids and supportive measures. Workup was unremarkable; therefore, a kidney biopsy was done. The biopsy specimen concluded the diagnosis of WRN. The patient was started on prednisone without any effect and then intermittent hemodialysis. Our case highlights the rare instance in which the cause of nephropathy is warfarin. If an early diagnosis had been made, the patient might have had a better prognosis; therefore, it is essential to have a high index of clinical suspicion when a patient presents with supratherapeutic INR and acute kidney injury (AKI) not getting better.