Two Methods for Intraplatelet Serotonin Evaluation: Their Use in Thrombocytosis

The content of platelet dense bodies is considered to be decreased in thrombocytosis associated myeloproliferative disorders and normal in reactive thrombocytosis. Intraplatelet serotonin i.e., 5-hydroxytryptamine (5HT), content is usually considered a particularly good marker. We report our experience of platelet 5HT levels evaluated by radioimmunoassay (RIA) and fluorimetric assays in patients with high platelet counts due to essential thrombocythemia (48 patients) or reactive thrombocytosis (34 patients). The diagnosis of essential thrombocythemia was made according to Polycythemia Vera Study Group criteria. A significant statistical difference was observed in serotonin platelet content between essential thrombocythemia and secondary thrombocytosis patients both with fluorimetric and RIA assays. On the contrary, no difference was evident between reactive thrombocytosis patients and normal control subjects. However, a significant difference was observed between 5HT in serum and platelet pellets when evaluated by RIA. Statistical analysis with the X2 test showed that the sensitivity of the fluorimetric assay is slightly higher than that of the RIA assay; however, specificity is about the same with the two methods. It is possible that the two assays measure different molecules. At any rate, the fluorimetric assay seems to be better in evaluating the platelet content of 5HT at least in patients with high platelet counts. Key Words: Thrombocytosis—Serotonin.