Vox Sang. zyxwvutsr 40: suppl. 1, pp. zyxwvuts 48-54 (198 1) zyxwvut Platelet Sizing: Value in Quality Control of Platelet Concentrates zyxwv Laurence Corash, Brenda Shafer National Institutes of Health, Hematology Service, Clinical Center, Clinical Pathology Department, Bethesda, Md., USA The biologic significance of platelet vol- ume distribution remains a controversial is- sue. At the heart of this controversy is the biologic significance of platelet heterogenei- ty. Any discussion of platelet size as it per- tains to assessment of platelet concentrates must, therefore, start with this basic issue. Data obtained in our laboratory during the past 6 years supports one concept of platelet heterogeneity and is relevant to the issue that is the focus of this forum. There is general agreement that platelets are heterogeneous with respect to physical, biochemical, and functional properties. It is as to the cause of the heterogeneity that opinions diverge. There are two basic schools of thought to explain these observa- tions: (1) platelet heterogeneity is due to aging changes in the peripheral circulation, and (2) platelet heterogeneity is solely a function of events during thrombocytopoie- sis, which simply states that different mega- karyocyte ploidy classes give rise to different types of platelets. The first proposition has its roots in the studies performed with animals made thrombocytopenic by heterologous anti- platelet antisera [l]. During the recovery phase, these animals produce platelets which are larger in size than their normal steady-state mean platelet volumes. The hu- man analogue is the patient with autoim- mune thrombocytopenia where radioiso- topic platelet survival is well-documented to be shortened, and large platelets are ob- served [2]. Based upon the assumption that these platelets are young platelets and that under steady-state unstressed conditions platelets appear to age in the peripheral cir- culation via a linear, senescent process, it was proposed that platelet size was an age- related property. Karpatkin [3] and Gins- burg and Aster zyx [4] developed methods to separate large platelets which are also heav- ier and thus could be isolated by centrifuga- tion in a variety of density media. A number of laboratories have reported data to support the concept that the larger, more dense platelets had ultrastructural, biochemical, and functional properties dif- ferent from lighter smaller platelets 14-63. Evidence to suggest that the larger platelets were preferentially sequestered by the spleen has also been reported [7]. Supportive data