Idiopathic thrombocytopenia with giant platelets.

Long-lasting, possibly constitutional thrombocytopenia, characterized by the presence of giant platelets, was found in a young woman. Conventional methods underestimated the number of circulating platelets and yielded erroneously elevated white cell counts. Platelet dysfunction was suggested by mild bleeding, prolongation of the Ivy bleeding time, and impaired platelet aggregation by collagen, adenosine diphosphate and adrenaline. The reported data suggest that this patient has a unique abnormality of platelet production.