Relation Between Platelet Volumes and Platelet Kinetics in Idiopathic Thrombocytopenic Purpura(ITP)

Platelet volume distribution and appearance rate of megathrombocytes were measured with Coulter counter Model-B in 24 patients with ITP during platelet kinetic studies. Normal range of platelet volumes in EDTA-blood is as follows: mode; 6.8 ±0.8 μm3 (mean ± 1 SD), median; 7.6 ±0.8 μm3 and mean volume; 9.4 ±1.1 μm3. In 15 patients platelets were increased in mean volumes, 8 patients showed normal size and one patient decreased in mean volumes. Increase of megathrombocytes (larger than 14 μm3) was noted in 14 cases. Remaining 10 cases showed normal appearance rate of megathrombocytes (15 ±4.7%). In 5 patients, highest peak was deviated to the smaller elements although the mean volumes were remained in normal range or increased. These findings suggest that at least two population of platelets are present simultaneously in these cases. No close correlation was noted between platelet volumes and platelet counts, mean platelet survival time or platelet turnover. The appearance rate of megathrombocytes also had no correlation with the results of platelet kinetics. Three out of 11 cases whose platelet counts increased to the normal after splenectomy- showed still larger platelet volumes than the normal. It could be concluded that young platelet could be of variable size in ITP and that it might be impossible to suspect the amounts of effective platelet production from the platelet volumes or the appearance rate of megathrombocyte s.