Reticulocyte subpopulations and reticulocyte maturity index (RMI) rise as body iron status falls

To investigate the influence of body iron status on reticulocyte subpopulat ions and reticulocyte maturity index (RMI), we measured serum iron markers, fluorescent intensity of reticulocytes, and serum transferrin receptor (sT fR) concentrations in 374 females aged 14-19 years. Reticulocyte subpopulat ions were analyzed by flow cytometry, end sTfR concentration was measured b y enzyme immunoassay. There were no significant differences in the values o f reticulocyte subpopulations and RMI between ferritin alone-depleted group and healthy controls. However, middle- and high-fluorescence reticulocytes and RMI were significantly higher in both the serum iron- and serum ferrit in-depleted groups than in the ferritin alone-depleted group. Middle-fluore scence reticulocytes and RMI increased gradually as the body iron store was depleted and were 3.4- and 3.6-fold higher, respectively, than normal cont rols, when the subjects attained a frank iron-deficiency anemia. There were no significant changes in the values of red blood cells or total reticuloc yte counts during iron-depleted states. The mean value of sTfR (3.98 mg/l) in the subjects with RMI greater than or equal to 1.5% was significantly hi gher than that (2.26 mg/l) in the subjects with RMI < 1.5% (P < 0.01), The sTfR concentration correlated significantly with RMI (r = 0.61, P < 0.01) a nd middle-fluorescence reticulocytes (r = 0.59, P < 0.01), In short, body i ron depletion induces elevation of immature reticulocyte fractions and RMI, Am. J. Hematol, 67:130-135, 2001. (C) 2001 Wiley-Liss, Inc.