Significance of Platelet Size and Shape Changes in Man

Platelet volume, shape and diameter were measured by thrombocrit, light- and electron-microscopy and electronic techniques in over 500 selected patients with disorders of thrombopoiesis and haemosta-sis. Mean cell volumes (MCVs) estimated by these independent methods agreed well. Median MCV of 100 random control subjects was 10.3 fl (two GST) range 8.51–12.46 fl), count was 233,000/μ1 (1.60–3.40 × 105), thrombocrit was 0.25% (0.20–0.31%) and geometric standard deviation (GSD) of volumes was 1.61 (1.56–1.67). But selected healthy subjects had congenitally smaller or much larger platelets, reciprocal variation in count but normal thrombocrit as strikingly illustrated by a new thrombocrit method permitting microhematocrit packing of all platelets from 1 ml whole blood with morphometrically proven absence of plasma trapping. Extreme MCV deviations were rare and mainly congenital e.g. ≈ 50 fl, ≈ 35 fl and ≈ 20 fl in the Davidson (3) May Hegglin (2) and Mediteranean (> 20) macrothrombocytopenias ; 5 fl in Wiskott Aldrich (4); up to 30 fl in transient macrothrombocytopenia during severe infection or hypoxia (4) and up to 40 fl in dysthrombocytosis of the blast crisis of the myeloproliferative syndrome (3). Acute reversible disc-sphere transformation induced by EDTA in health was shown to be isovolumetric citrate platelets being discoid at 22° C with an axial ratio of 0.23 (0.18–0.27). In accord with Coulter theory effective electric volume of EDTA platelets exceeded that of citrate cells by a factor of 1.28 (1.181–1,382) – a measure of platelet shape differences termed E/C ratio. During lesser MCV deviations platelets appearance in blood films and during electronic sizing of citrate cells was dominated by shape heterogeneiety the E/C ratio correlating negatively (P < 10-3) with increased platelet turnover because citrate platelets show pseudopodial activation and sphering. For example in over 20 patients with acute ITP, ≈ 8-fold increase in platelet turnover, normal or only slight increase in both thrombocrit MCV and electronic size of EDTA platelets, electronic size and GSD of citrate platelets was increased, E/C ratio was consistently below 1.08 and many platelets were spread in blood films. In other acquired disorders MCV deviations were also usually minor.