Babesiosis-induced acute kidney injury with prominent urinary macrophages.

Babesia is an obligate intracellular erythrocyte parasite that can infect humans. Severe symptomatic disease from massive hemolysis and multiorgan system failure, including acute kidney injury (AKI), occurs. Acute tubular injury from a combination of volume depletion and heme pigment toxicity from profound hemolysis is the most common cause of AKI. We present a case of severe babesiosis complicated by dialysis-requiring AKI with the unique finding of large macrophages containing engulfed erythrocyte fragments in urine sediment. This urinary finding raised the possibility of another diagnosis distinct from acute tubular injury. Subsequent kidney biopsy demonstrated infection-associated acute interstitial nephritis.