[Macrothrombocytosis and idiopathic thrombocytopenic purpura: effect of anticoagulant and prior fixation on the determination of platelet volume using the Coulter system].

This study was designed to evaluate the importance of anticoagulants and of prior fixation on the Coulter Counter platelet size determination in macrothrombocytosis occurring in patients affected with an idiopathic thrombocytopenic purpura (ITP). Native blood was sampled either in an iso-osmotic glutaraldehyde fixative solution at 37 degrees C or in standard citrated or EDTA vacutainers. Platelet size increased from the fixed whole blood sample to the unfixed standard citrate and EDTA samples. There was a good correlation between the three determinations. Of the 23 ITP cases 10 presented large sized platelets both in citrated and in fixed whole blood samples; however 4 of these patients presented a platelet size in the normal range in the EDTA samples. These results show that citrated blood samples are preferable to EDTA samples for detecting an increased platelet size in ITP and that ITP macrothrombocytosis does not result from an abnormal hypervolumetric shape change occurring in vitro after sampling.