MPL and Thrombocytopenia: Previously, we demonstrated that plasma FXIII-A levels are normal in the thrombocytopenic Mpl−/− and BClxPlt20/Plt20 mice.3 However, we did not assay platelet FXIII-A in the Mpl−/− mouse, in which depletion of ≈94% platelets and their precursors results from knockout of the thrombopoietin receptor.24 Here, we have shown that the amount of FXIII-A per platelet has not increased to compensate for thrombocytopenia.