Hemolysis-associated hemoglobin cast nephropathy results from a range of clinicopathologic disorders.

Intravascular hemolysis is relatively rare but can lead to acute kidney injury (AKI), from increased destruction of erythrocytes and release of free hemoglobin. Since hemolysis and hemoglobinuria are known causes of acute kidney injury we sought to define clinicopathologic findings and outcomes of patients with hemolysis-associated hemoglobin cast nephropathy through a retrospective analysis of 27 cases. The mean patient age was 47 years (range 19-79) and the female-to-male ratio was 1.3:1. All patients presented with AKI with a mean serum creatinine of 8.0 (range 2.9-17.0) mg/dL. Etiologies included autoimmune hemolytic anemia (30%), medication (26%), paroxysmal nocturnal hemoglobinuria (7%), procedural/mechanical causes (7%), transfusion of incompatible blood (4%), toxin ingestion (4%), disseminated intravascular coagulation (4%), and hemoglobinopathy (4%). All biopsies showed acute tubular injury and pigmented, proteinaceous casts characterized by positive hemoglobin immunohistochemistry. After a mean follow-up of nine months (range 0.5-26), the mean serum creatinine was 1.3 (range 0.6-3.3) mg/dL, with 78% of patients returning to normal kidney function. Thus, based on our clinicopathologic case series, hemolysis-associated hemoglobin cast nephropathy is an important entity for clinicians and pathologists to recognize as treatment hinges upon elimination of the pathogenic driver of intravascular hemolysis.