BackgroundPatients with pathogenic variants in RASGRP2 (inherited platelet disorder [IPD]-18) have normal platelet counts but show impaired platelet aggregation due to diminished activation of αIIbβ3 integrin. This defect results in moderate-to-severe bleeding episodes, especially following surgical procedures, which require patients to be transfused with platelets and/or prohemostatic agents. We recently demonstrated that hemostatic efficacy of transfused platelets is limited by dysfunctional endogenous platelets in a mouse model of IPD-18 (Rasgrp2−/− mice), as dysfunctional platelets were recruited to the forming hemostatic plug but did not participate in clot contraction. Consequently, higher amounts of transfused platelets were required to outcompete these dysfunctional cells and to reverse bleeding. ObjectivesWe here studied the usefulness of thromboelastography (TEG) with platelet mapping (TEG-PM), a method to evaluate platelet-dependent clot contraction, for ex vivo monitoring of the hemostatic potential in Rasgrp2−/− mice transfused with various amounts of wild-type (WT) platelets. ResultsRasgrp2−/− whole blood samples did not contract in TEG-PM, consistent with a critical role of this protein in αIIbβ3 activation. Addition of WT platelets improved TEG parameters (K time, α angle, and maximum amplitude) in a ratio-dependent manner, consistent with our recent in vivo studies showing impaired hemostasis at a 5:1 but not at a 2:1 ratio of mutant to WT platelets. K and α values were identified as better predictors of transfusion efficacy than maximum amplitude, the most platelet-dependent TEG parameter. ConclusionThis proof-of-concept study supports the use of TEG-PM to monitor platelet transfusion ratios and hemostatic potential in IPD-18 and potentially other platelet disorders.