Platelet phagocytosis as a cause of pseudothrombocytopenia

Abstract

A 43-year-old man with no history of bleeding or bruising had a routine blood count performed prior to angiography. The automated platelet count on an impedance-based instrument was 108 3 10 9 L 21. The rest of the blood count was normal. Because of the unexpected thrombocytopenia, a blood film was examined. This showed extensive phagocytosis of platelets (Image 1). There was limited platelet satellitism, suggesting that this may have been the first stage of the process (top left image). In some cells, phagocytic vacuoles were clearly apparent (bottom right image). An in vitro phenomenon was suspected. A repeat blood sample was therefore taken, and a film prepared with no exposure to anticoagulant showed no phagocytosis. After a brief exposure to EDTA, occasional neutrophils showed satellitism and phagocytosis, and the platelet count was 158 3 10 9 L 21. By 4 hr, phagocytosis was extensive. The patient proceeded to an uneventful angiogram.

Platelet morphology

“…The examination of a peripheral blood (PB) smear should be requested in every case of unexplained thrombocytopenia or thrombocytosis. First, the morphological analysis should include the estimation of the number of platelets in order to confirm the platelet count determined by the haematology analyser, and to rule out causes of spuriously low platelet counts due to platelet aggregates, platelet satellitism or platelet phagocytosis [1][2][3][4]. The identification of pseudothrombocytopenia (PTP) due to anticoagulantinduced platelet aggregation is crucial, because a misinterpretation as a "true" thrombocytopenia may lead to serious diagnostic and therapeutic consequences such as bone marrow biopsy, initiation of corticosteroid therapy, platelet transfusion or even splenectomy [2].…”