Acute kidney injury as a harbinger of paroxysmal nocturnal hemoglobinuria in an unsuspected case.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal disorder of hematopoietic stem cells characterized by complement-mediated intravascular hemolysis. Renal involvement, though often subclinical, can occasionally present as acute kidney injury (AKI). We report a case of a 24-year-old female who presented with AKI without any clinical or laboratory evidence of hemolysis. Kidney biopsy revealed acute tubular necrosis with hemosiderin deposition, suggestive of chronic hemolysis. The patient recovered with supportive care, and a diagnosis of PNH was not confirmed until 6 years later, following evaluation for anemia. Flow cytometry at that time revealed CD55 and CD59 deficiency, confirming PNH. This case highlights the diagnostic challenge of PNH when it presents atypically and emphasizes the importance of recognizing renal hemosiderosis as a potential early clue. In patients with unexplained AKI and biopsy evidence of hemosiderin deposition, PNH should be considered even in the absence of overt hemolysis or classical symptoms.