Box plots of platelet count vs donor myeloid chimerism at 1 and 2 years and 3 to 5 years after HCT. Donor myeloid chimerism: full, >95%; high-level, 50% to 95%; low-level, 5% to 49%. Recovery of platelet counts after HCT was related to the degree of donor myeloid chimerism. Specifically, platelet counts for patients who had low-level (5% to 49%) donor myeloid engraftment remained inferior to those who had attained full (>95%) donor myeloid engraftment at 1 year (P < .0001), 2 years (P < .0001), and 3 to 5 years (P = .0002). In addition, platelet counts were lower in patients with low-level (5% to 49%) donor myeloid engraftment compared with those who attained high level (50% to 95%) donor myeloid engraftment at 1 year after HCT (P = .011); however, this was not significant at 2 or 3 to 5 years after HCT. All other pairwise comparisons were not significant.