The proportion of reticulated platelets is higher in bone marrow than in peripheral blood in haematological patients

Since the detection that platelets originate from megakaryocytes (MK), the site of megakaryocyte fragmentation has been disputed. Some authors have ev en postulated that platelets are solely produced in the lungs. Thus, we hav e directly measured platelet generation in the bone marrow (BM) by comparin g the relative number of young RNA-containing, so-called reticulated platel ets (%RP) in the BM and in the peripheral blood (PB). Two separate prospect ive, cross sectional trials have been conducted in patients routinely under going BM biopsies fbr diagnostic purposes. In the first part of the study 3 0 patients with stem cell or bone marrow transplantation were examined. The second part of the study was performed in 62 haematological patients visit ing the outpatient's clinic. Median %RP were higher in BM than in PB (p < 0 .001). In the second part of the study the difference averaged 133% (interq uartile range: 30-383%. There was a moderate correlation between %RP in BM and in PB (r = 0.67; p < 0.001). The absolute number of RP in PB correlated weakly with the number of megakaryocytes (0.42; p = 0.001), which was due to a correlation between the platelet counts and the megakaryocyte counts ( r = 0.55; p < 0.001 in biopsies). Two patients with autoimmune antibodies a gainst GPIIb/IIIa exhibited 10% and 16% RP in PB, and had 29% and 59% RP in BM, respectively. It is concluded that the relative number of RP is signif icantly higher in BM than in blood. This supports the notion that platelets are at least in part released from MK in the bone marrow, particularly in patients suffering from immune thrombocytopenia.