| Abstract: | Mean megakaryocyte ploidy, mean platelet volume, and platelet count were measured during 17 courses of chemotherapy for acute nonlymphocytic leukemia. During the myelosuppression from chemotherapy, all three variables fell; during recovery, megakaryocyte ploidy rose 1–2 days before platelet volume, which in turn rose 1–2 days before platelet count. Serial platelet volumes and counts of these patients were compared to the nomogram of the inverse nonlinear relation between platelet count and platelet size in reference subjects. Platelet volume became inappropriately small before platelet count fell substantially and remained small through most of the thrombocytopenic nadir. The end of the nadir was predictable 1–2 days after platelet volume increased to lie congruent with the reference nomogram. Changes in thrombopoiesis appear to occur sequentially in megakaryocyte ploidy, platelet volume, and platelet count. Changes in platelet count, and therefore the appearance of duration of the thrombocytopenic nadir, can be predicted by 1–2 days with platelet volume and 3–4 days with megakaryocyte ploidy. As platelet count rose, despite the continuing predominance of “young” platelets, MPV fell, suggesting that megakaryocyte stimulation as well as platelet age affects platelet size. |
