Significance of the ratio of reticulocyte subpopulations in bone marrow and peripheral blood from patients with myelodysplastic syndromes.

Abstract

Flow cytometric analysis enables evaluating maturation of reticulocytes by quantitating the fraction of reticulocytes within low-, middle-, and high-fluorescence intensity regions (LFR, MFR, and HFR, respectively) [1]. The immature reticulocyte fraction (IRF), the sum of MFR and HFR, which corresponds to young reticulocytes released prematurely, is a useful parameter to evaluate the erythropoietic activity in anemia. The reticulocyte maturity index (RMI) is calculated from the proportion of reticulocyte subpopulations and can be used as the earliest and most sensitive predictor of erythropoiesis [2]. The premature destruction of erythroid precursors in the medullary cavity is termed ineffective erythropoiesis and occurs normally in less than 10% of the developing cells [3]. However, loss of much larger numbers of cells is seen in myelodysplastic syndromes (MDS), megaloblastic anemia, hemoglobinopathies, and several rare congenital anemias such as congenital dyserythropoietic anemias. MDS are bone marrow stem cell disorders characterized by ineffective hematopoiesis leading to blood cytopenias despite the presence of a cellular marrow and a propensity towards leukemic transformation [4]. There have been few studies, which have closely examined the production of reticulocytes in the bone marrow from patients with MDS and the significance of the ratio of reticulocyte subpopulations. Hence, in this study we assessed the immature reticulocytes and RMI using flow cytometry in both bone marrow and peripheral blood from MDS patients and compared the values to those of non-MDS patients as well as healthy controls. The number of mature reticulocytes and immature reticulocyte subpopulations were measured with flow cytometry in bone marrow and venous blood samples from 72 MDS patients and 65 controls (70 males, 67 females, age range: 51–76 years). The MDS patients included 31 with refractory anemia (RA), 12 RA with ringed sideroblasts, and 29 RA with excess of blasts. We studied 34 ageand gender-matched nonanemic individuals as controls, who had no hematologic disorders. As additional controls, we also assessed the reticulocytes in the bone marrow from non-MDS patients (n=31) with anemia but with no evidence of ineffective erythropoiesis such as carcinoma (n=12) and lymphoma (n=19) not involving the bone marrow. Because reticulocyte production is affected by the degree of anemia, we compared MDS patients not only to the healthy controls but also to non-MDS patients who showed similar hemoglobin levels to MDS patients. Bone marrow and peripheral blood specimens were obtained at initial presentation from patients, and none of the patients had received any specific therapy prior to the study. Complete blood cell count was determined using an electronic counter (SE 9000, Sysmex, Kobe, Japan). Reticulocytes and their subpopulations were automatically analyzed by flow cytometry (R-3000, Sysmex, Kobe, Japan). The corrected reticulocyte count was calculated, based on a normal hematocrit of 45%, using the following formula: corrected reticulocyte (%) = (subject’s hematocrit/45) reticulocyte count (%). RMI was calculated using the equation: RMI = (MFR + HFR) 100/LFR and expressed as the percentage [5]. We compared the values of reticulocytes, corrected reticulocytes, IRF, and RMI of bone marrow (BM) to those of peripheral blood (PB). The Mann-Whitney U test was used to compare differences of mean values. P<0.01 was considered statistically significant (Table 1). There were no significant differences in the mean values of total reticulocytes between MDS patients and control group, nor between MDS patients and non-MDS patients in bone marrow. However, immature reticulocyte subpopulations in bone marrow from patients with MDS J. W. Choi ()) · S. H. Pai Department of Laboratory Medicine, College of Medicine, Inha University, 400-711 Inchon, South Korea e-mail: jwchoi@inha.ac.kr Tel.: +82-32-8902503 Fax: +82-32-8902529