A case of pseudothrombocytopenia after infusion of abciximab in vivo and anticoagulant-independent platelet clumping after rechallenge with abciximabin vitro

A 45-year old man was treated for unstable angina pectoris with percutaneou s transluminal angioplasty and stenting of his left anterior descending cor onary artery. The procedure was followed by infusion of abciximab. The pati ent's automated platelet count in an EDTA-anticoagulated blood sample at ad mission to the hospital was normal, but dropped to 5 x 10(9)/l three hours after the procedure. The infusion of abciximab was stopped and the patient received platelet transfusions although there were no signs of bleeding. Tw o days later his platelet count was still low (37 x 10(9)/l) in an EDTA-ant icoagulated blood sample, but normal (193 X 10(9)/l) in a heparin-anticoagu lated sample. Platelet clumps were present only in the sample anticoagulate d with EDTA, and pseudothrombocytopenia was diagnosed. The patient's recove ry was uneventful. At follow-up visits four months and one year after disch arge from hospital, the patient's blood samples were anticoagulated with th ree different anticoagulants: EDTA, citrate and heparin. The platelet count was normal in all three samples but after mixing with abciximab in vitro i t dropped profoundly due to platelet clumping, regardless of the choice of the anticoagulant. Our report raises two points: (a) one needs to consider the possibility of pseudothrombocytopenia in a patient with a low automated platelet count after infusion of abciximab but without signs of bleeding, and (b) the in vitro results suggest that our patient who had initially res ponded to abciximab with pseudothrombocytopenia could develop true thromboc ytopenia after repeated exposure.