Giant (Bernard-Soulier) Platelets are Normal Sized in Circulation

Bernard-Soulier Syndrome (BSS) is a platelet disorder for which one of the characteristics is the appearance of “giant” platelets on peripheral blood smears. A comparison is made between the shape distributions of platelets obtained from normal (9) and BSS (3) donors. Geometric parameters are evaluated from a cinematographic analysis of freely rotating glutaraldehyde-hardened and unfixed platelets and of platelets on blood smear. On blood smear, normal platelets have a mean diameter of 1.8 ± 0.2 μm, where 10% have a diameter greater than 2.5μm (Weiss, et al (1974). Am. J. Med. 57: 920). On the other hand, BSS platelets are significantly larger, having a mean diameter of 3.3 + 0.7/μm, with 80% having a diameter greater than 2.5μm. These observations are consistent with all published reports concerning BSS platelets and suggest donors homozygous for this disorder (Bithell, et al (1972) N. Y. Acad. Sei. 201: 145). In contrast, the freely circulating disc-form of the BSS platelet is essentially indistinguishable from a normal platelet: mean diameter and thickness of 3.2 ± 0.3μm, and 1.4 ± 0.4 μm respectively, as compared with 3.2 ± 0.3 μm and 1.1 ± 0.4 μm for normal platelets. It is concluded that the giant size of BSS platelets results from abnormal behaviour of these platelets during the preparation of the blood smear.