Spurious thrombocytopenia during pregnancy.

Thrombocytopenia in four healthy pregnant women proved to be spurious and caused by in vitro clumping of platelets (three) or adherence of platelets to granulocytes (one) in the presence of edetic acid used to anticoagulate the blood. All had normal vaginal deliveries without unusual bleeding. One of the newborns transiently exhibited the phenomenon of platelet clumping in vitro, probably due to transplacental transfer of the platelet agglutinin from the mother. Recognition of these laboratory artifacts is important to avoid unwarranted investigations and inappropriate management of the mother and infant. Careful examination of a blood smear in all thrombocytopenic patients is the best safeguard against being misled by spurious thrombocytopenia.