Altered platelet phospholipid-dependent thrombin generation in thrombocytopenia and thrombocytosis.

Platelet phospholipid dependent thrombin generation was determined in 20 patients with thrombocytosis, 18 with thrombocytopenia, and 25 normal controls, using a quantitative chromogenic assay. Platelets from patients with myeloproliferative disorders displayed normal lag times to 20 nM thrombin concentration but increased thrombin potentials, even when corrected for platelet size. Platelets from patients with reactive thrombocytosis supported normal thrombin generation. ITP platelets were large, with a proportionate increase in thrombin potentials, but very short lag times to 20 nM thrombin concentration. Following marrow ablation there was a progressive loss of activation-induced enhancement of thrombin generation. Platelets from patients with idiopathic aplastic anaemia supported normal thrombin generation. These findings indicate that platelet phospholipid-dependent thrombin generation is altered in many patients with a variety of quantitative platelet disorders, and this may be an important determinant of the clinical expression of these disorders.