Reticulocyte maturation index: a prediction tool for recovery in post bone marrow and peripheral blood stem cell transplant patients

Abstract

Erythropoietic response is the first indication of bone marrow recovery following bone marrow or peripheral blood stem cell transplantation. Manual reticulocyte counting has not only proven to be outdated but an extremely crude method of analysis, particularly if accurate and reliable means of assessing erythroid response is required to assess bone marrow recovery. Automated methods allow for the quantification of maturation within each reticulocyte, by measuring the amount of RNA present. The method of choice for our reticulocyte analysis was the Reticulocyte Maturation Index (RMI). The RMI was obtained by dividing the number of immature reticulocytes counted by the total number of reticulocytes counted producing a reportable value of International Units (IU). A normal Reticulocyte Maturation Index is 0.20 to 0.50 IU. The aim of the study was multifold. We wanted to prove that the Reticulocyte Maturation Index (RMI) is indeed the fastest means to assess bone marrow recovery in various types of transplants, including Bone Marrow Transplant (BMT) and Peripheral Blood Stem Cell Transplant (PBSCT). We also wanted to draw comparisons between allogeneic and autologous transplants, as well as further assessing different disease types. This was done by measuring the Reticulocyte Maturation Index (RMI), Absolute Neutrophil Count (ANe) and the Platelet Count (PLT) within the various groups. We further wanted to assess the effect of preconditioning treatment, Mononuclear Counts (MNC) and Colony Forming Unit - Granulocyte and Monocyte Counts (CFU-GM) on the early RMI response. These comparisons resulted in a need to establish a working range to determine patients response therein, and final outcome of the transplants. Finally we wanted to establish whether the "day 14" marrow biopsy is necessary, particularly if the three peripheral blood parameters, RMI, ANC and PLT were used as routine procedure following transplantation. The Reticulocyte Maturation Index (RMI) was measured on the Coulter EPICS ProfIle II flow cytometer; the ANC and PLT were measured on the Technicon H2 Haematology System. All other results such as the Mononuclear Counts (MNC), Colony Forming Unit - Granulocyte and Monocyte counts (CFU-GM), "day 14" and "day 28" bone marrow biopsies were retrieved from laboratory records. Forty nine transplant patients were evaluated for RMI over a period of six months, at the Department of Haematology, Groote Schuur Hospital, Cape Town. Four patients failed to engraft; and were not used in the calculations; but were evaluated as an aspect of the study in the final analysis. Forty five patients were analysed to establish the values used in the study, these patients were divided into eleven groups.