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

Summary. Background: Theplateletcountvariesconsiderablybetween individuals, butwithin an individual the plateletcountis remarkably stable over time. Mechanisms controlling theplatelet count are not yet established. Objective: In the presentstudy, we tested the hypothesis that the liver is important incontrollingthecirculatingplateletcount,astheliveristhemainproducer of thrombopoietin. Methods: We compared theplatelet count prior to and after liver transplantation in> 250patientstransplantedforfamilialamyloidoticpolyneur-opathy (FAP). In contrast to most patients undergoing livertransplantation, patients with FAP have normal liver functionbefore transplantation. Furthermore, we compared plateletcounts in 89 living liver donors with the platelet count in therecipientsofthesegrafts.Finallywecomparedplateletcountsindonor-recipient pairs of hematopoietic stem cells. Results andconclusions: The platelet count prior to transplantation corre-lated with the platelet count at 3 or 12 months after transplan-tation in patients with FAP ( r = 0.48, P < 0.0001 at3 months, r = 0.39, P < 0.0001 at 12 months), whereas theplatelet count in a living liver donor did not correlate with theplatelet count in the recipient at 3 or 12 months aftertransplantation (r =0.16,P = 0.26 at 3 months, r = 0.11,P = 0.30at12 months).Theplateletcountofrelateddonorsofhematopoieticstemcellscorrelatedwiththeplateletcountintherecipient after transplantation ( r = 0.25, P = 0.011). Conclu-sions: These results suggest that the liver, in spite of being theprime producer of thrombopoietin, does not dictate thecirculating platelet count, whereas the bone marrow doesappear to play a role.Keywords: bone marrow transplantation, homeostasis, livertransplantation, platelet.IntroductionBlood platelets play a pivotal role in hemostasis and throm-bosis as evidenced by the bleeding tendency of patients withqualitative or quantitative platelet defects, and the efficacy ofanti-platelet drugs in the primary or secondary prevention ofarterial thrombosis. The average platelet count in humansvaries substantially between individuals, ranging from 150 000to 350 000 lL