Spuriously high platelet counts caused by intravascular haemolysis
Introduction - intravascular hemolysis is accompanied by the formation of erythrocyte fragments, which can be recognized by the hematology analyzer as platelets. The aim of the study was to present possible errors of platelets count estimated in patients with intravascular hemolysis. Material and methods. Clinical reports of two patients with intravascular hemolysis were presented. In both patients hematological analyzer falsely estimated the increase of platelets count. In experimental part intravascular hemolysis was reproduced in vitro by heating and mechanical destruction of red blood cells (RBC) in RBC concentrates. The relationship between hemolysis and platelets count was investigated. Thermal hemolysis was achieved by heating 11 samples of RBC concentrates in a thermostat at 50 °C. Mechanical hemolysis was achieved by forcing and aspiration of 10 samples of RBC concentrates through a DTS column (CliniMACS Plus, Germany). Hemolysis was confirmed by increased concentration of free plasma hemoglobin. Blood cell count was performed by Sysmex XP-300. The Mann-Whitney U-criterion was used to assess the differences between two independent samples. The difference between two dependent samples was assessed by the Wilcoxon criterion. Results. A discrepancy between hemorrhagic syndrome and platelets count (respectively, 296⋅10/l and 155⋅10/l) estimated by hematological analyzer was revealed in both patients with intravascular hemolysis associated with extracorporeal membrane oxygenation and thrombotic microangiopathy. However, platelets count, estimated by microscopy was 11⋅10/l and 13⋅10/l, respectively. In samples of RBC concentrates with thermal hemolysis the platelets count increased from a median of 2⋅10/l to a median of 486⋅10/l, in RBC concentrate samples with mechanical hemolysis - from the median 0⋅10/l to the median 60,9⋅10/l. The source of platelets count errors was incorrectly identification of RBC fragments as platelets by hematological analyzer. Conclusion. Intravascular hemolysis requires blood platelet count by visual method.