Occurrence and clinical significance of pseudothrombocytopenia during abciximab therapy

OBJECTIVES This study determined the incidence of pseudothrombocytopenia du ring abciximab therapy administered for percutaneous coronary interventions and compared the clinical course of patients with pseudothrombocytopenia w ith the clinical courses of patients with thrombocytopenia and patients wit h normal platelet counts. BACKGROUND Although pseudothrombocytopenia has been previously reported dur ing therapy with abciximab, the incidence and significance of this occurren ce are unknown. The failure to differentiate pseudothrombocytopenia from th rombocytopenia could lead to unnecessary interruption of abciximab infusion s or to platelet transfusions. METHODS The incidences of pseudothrombocytopenia and thrombocytopenia were determined in four large placebo-controlled abciximab trials: c7E3 Fab Anti platelet Therapy in Unstable Refractory Angina (CAPTURE), Evaluation of 7E3 for the Prevention of Ischemic Complications (EPIC), Evaluation of Percuta neous Transluminal Coronary Angioplasty to Improve Long-term Outcome of c7E 3 GpIIb/lIIa Receptor Blockade (EPILOG) and Evaluation of Platelet IIb/IIIa Inhibitor for Stenting (EPISTENT). The clinical features, bleeding complic ations and major clinical outcomes of patients with pseudothrombocytopenia and those with thrombocytopenia were compared with each other and with thos e of patients with normal platelet count. RESULTS Pseudothrombocytopenia occurred in 2.1% (95% confidence intervals [ CI]: 1.7%, 2.5%) of of abciximab-treated patients and in 0.6% of placebo-tr eated patients (p < 0.001). Thrombocytopenia occurred in 3.7% (95% CI: 3.2% , 4.2%) of abciximab-treated patients and in 1.8% (95% CI: 1.3%, 2.3%) of p lacebo-treated patients (p < 0.001). Patients with thrombocytopenia had sig nificantly higher rates of major bleeding, major decreases in hemoglobin an d increased transfusion requirements of both blood and platelets compared w ith those without thrombocytopenia. By contrast, pseudothrombocytopenic pat ients did not differ from patients with normal platelet counts in any of th e measures of blood loss or transfusion requirements. Thrombocytopenic pati ents, but not those with pseudothrombocytopenia, had increased rates of rev ascularization at 30 days and six months. As previously reported, there was also a higher rate of death and myocardial infarction in the thrombocytope nic patients. CONCLUSION Pseudothrombocytopenia is the cause of more than one third (36.3 %) of low platelet counts ill patients undergoing coronary interventions wh o are treated with abciximab. This study demonstrates that pseudothrombocyt openia is a benign laboratory condition that does not increase bleeding, st roke, transfusion requirements or the need for repeat revascularization. It is important to recognize pseudothrombocytopenia so that the beneficial ef fects of abciximab are not lost by premature termination of therapy. (J Am Coil Cardiol 2000; 36:75-83) (C) 2000 by the American College of Cardiology .