Serotonin in blood: assessment of its origin by concomitant determination of β-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, β-thromboglobulin (β-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 β-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 β-TG.