The circulating platelet count is not dictated by the liver, but may be determined in part by the bone marrow: analyses from human liver and stem cell transplantations.

The platelet count varies considerably between individuals, but within an individual the platelet count is remarkably stable over time. Mechanisms controlling the platelet count are not yet established. In the present study, we tested the hypothesis that the liver is important in controlling the circulating platelet count, as the liver is the main producer of thrombopoietin. We compared the platelet count prior to and after liver transplantation in >250 patients transplanted for familial amyloidotic polyneuropathy (FAP). In contrast to most patients undergoing liver transplantation, patients with FAP have normal liver function before transplantation. Furthermore, we compared platelet counts in 89 living liver donors with the platelet count in the recipients of these grafts. Finally we compared platelet counts in donor-recipient pairs of hematopoietic stem cells. The platelet count prior to transplantation correlated with the platelet count at 3 or 12 months after transplantation in patients with FAP (r=0.48, P<0.0001 at 3 months, r=0.39, P<0.0001 at 12 months), whereas the platelet count in a living liver donor did not correlate with the platelet count in the recipient at 3 or 12 months after transplantation (r=0.16, P=0.26 at 3 months, r=0.11, P=0.30 at 12 months). The platelet count of related donors of hematopoietic stem cells correlated with the platelet count in the recipient after transplantation (r=0.25, P=0.011). These results suggest that the liver, in spite of being the prime producer of thrombopoietin, does not dictate the circulating platelet count, whereas the bone marrow does appear to play a role.