Paroxysmal nocturnal hemoglobinuria mimicking thrombotic thrombocytopenic purpura treated 
using therapeutic plasma exchange：A case report

Abstract

Thrombotic thrombocytopenic purpura（TTP）is a well-known condition associated with hemolytic anemia. We report a case of paroxysmal nocturnal hemoglobinuria（PNH）that was initially suspected to be TTP based on the detection of fragmented red blood cells. A woman in her 60s presented to our hospital with fatigue. Laboratory findings indicated hemolytic anemia with 1.2％ fragmented red blood cells, elevated lactate dehydrogenase（LDH）and decreased haptoglobin levels, renal dysfunction, thrombocytopenia, and positive COVID-19 results. The clinical presentation suggested thrombotic microangiopathy, which led to a high index of clinical suspicion of TTP with COVID-19．LDH levels reduced following therapeutic plasma exchange; however, the platelet count only marginally improved. Analysis of red blood cell surface markers CD55 and CD59 revealed deficiencies, confirming the diagnosis of PNH. Although PNH typically does not alter red blood cell morphology, red blood cell fragmentation may occasionally occur, warranting an accurate differential diagnosis.