This 58-year-old African American male without significant past medical history presents with fatigue and weakness. During workup, he was found to have anemia, mild thrombocytopenia, elevated LDH, low haptoglobin and acute kidney injury. The serum creatinine at presentation was 5.5 mg/dl. A renal biopsy was performed and shows acute tubular injury with numerous granular and globular eosinophilic (Fig 1) and fuchsinophilic casts (Fig 2) within the tubular lumens. A myoglobin immunoperoxidase stain is negative (not shown) and a hemoglobin stain is diffusely positive within the pigmented casts. Otherwise, the glomeruli and vessels appear normal, without evidence of microangiopathy. These findings are indicative of intravascular hemolysis with hemoglobinuria. Immunohistochemical staining for hemoglobin and myoglobin is of utmost importance, given that the morphologic features of these two forms of cast nephropathy are indistinguishable.
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