Human platelet 5-hydroxyindoleacetic acid concentrations are meager and unlikely to be physiologically active or play a role in inflammation

OBJECTIVES: A crucial role for platelet 5-hydroxyindoleacetic acid (5-HIAA, the principal serotonin metabolite) in human immune response and inflammation has been claimed. We have attempted to assess the likelihood of such a role for platelet 5-HAA. To assess the concentration of 5-HIAA in human platelets, we have reviewed prior reports of platelet 5-HIAA concentrations and to measure 5-HIAA concentrations in human platelet-poor plasma (PPP) and platelet-rich plasma (PRP) samples. METHODS: = 68). RESULTS: = .872. Measured levels were consistent with most prior reports. DISCUSSION: Based on the observed PRP and PPP 5-HIAA concentrations, platelet 5-HIAA concentrations appear to be less than 1 ng/billion platelets. This compares to a typical mean concentration of human platelet serotonin of 600 ng/billion platelets. CONCLUSION: It appears that the platelet has only negligible amounts of 5-HIAA and that platelet 5-HIAA is unlikely to play a role in human immune response, in inflammation, or in any other aspect of human physiology.