[Platelet volume in essential thrombopenia].

The electronic method for measuring platelet volume using the Coulter Z BI Counter coupled with a Channelyser C 1000 has been standardized. The distribution of platelet volumes was studied in 28 cases of idiopathic thrombocytopenic purpura (ITP) and in 59 cases of thrombocytopenia attributed to a failure of platelet production. Results showed that the volumetric distribution curve of platelet rich plasma (PRP) was altered in 40 cases, by the presence of small particles interfering with platelets of small volume and/or by residual red cells modifying its terminal segment. These abnormalities seem linked to the degree of thrombopenia, but independent of its central or peripheral origin. A method of isolation and concentration of platelets in an albumin gradient allowed the restoration of the classical volume distribution in 24 cases out of 40. Simulated thrombopenias obtained by dilution of platelets in their own platelet poor plasma (PPP) showed that the abnormalities in the small volume range could be reproduced in vitro by modifying the proportion of platelets and of small residual elements in the PRP. When the albumin gradient method was used, the classical distribution of platelet volumes was found. Preliminary electron-microscopy studies show that the small elements in the PRP of thrombopenic subjects could be formed by red cell fragments. Cytoenzymologic studies should be able to confirm this. Volumetric parameters were determined from the asymmetric and unimodual distribution of platelets, either directly on PRP or after concentration and separation of platelets in an albumin gradient. They showed that platelet volumes were very often increased in ITP but also occasionnally in thrombopenia of attributed to a failure of production.