Serotonin in blood: assessment of its origin by concomitant determination of ß-thromboglobulin (platelets) and chromogranin A (enterochromaffin cells).

BACKGROUND: Serotonin is produced in enterochromaffin (EC) cells, taken up and stored in platelets and released during platelet activation. Measurement of platelet-poor plasma serotonin is difficult, mainly due to platelet activation during blood sampling. We aimed to establish a method to assess the influence of platelet release upon platelet-poor plasma serotonin measurement by concomitant determination of serotonin, ß-thromboglobulin (ß-TG) and chromogranin A (CgA). METHODS: Blood samples from patients with thrombocytosis, thrombocytopenia and small intestinal neuroendocrine (EC-cell) tumors (SI-NETs) as well as healthy volunteers were analyzed. We also measured serotonin in venous and arterial samples from patients undergoing coronary angiography to evaluate peripheral serotonin metabolism. RESULTS: Serotonin and CgA were significantly higher in patients with SI-NETs compared to all other groups implying EC cell origin of serotonin in patients with SI-NETs. We found that the serotonin concentration was similar in patients with thrombocytosis and thrombocytopenia, whereas plasma ß-TG was higher and lower respectively. A high EDTA concentration in the sampling tubes gave significantly lower serotonin concentrations. Serotonin concentrations did not differ between arterial and venous blood. CONCLUSIONS: Our methodology to measure platelet-poor plasma serotonin was appropriate. Blood platelet numbers did not affect the level of serotonin in contrast to ß-TG.