[Value of analyzing reticulocyte subpopulations in polycythemia]

The evaluation of the RNA content in reticulocytes by means of flow cytometry allows us to differentiate three reticulocyte populations by their degree of maturity: LFR, MFR and HFR. We have studied the value of those reticulocyte subpopulations for the differential diagnosis in polycythemia.

We have studied 25 polycythemia patients, 12 of these were diagnosed of polycythemia vera (PV) and 13 of secondary polycythemia (PS). Reticulocytes and their different reticulocyte populations were automatically analyzed by flow cytometry using the Sysmex R-2000 analyzer (TOA Corp. Japan). We calculated the reticulocyte maturity index (RMI) which is the percentage of the equation (MFR + HFR) x 100/LFR (9). We have also studied hemogram parameters (Hct, Hb, VCM, HCM, RDW, leukocytes and platelets), iron metabolism (serum iron, ferritin, transferrin and transferrin saturation index), and erythropoietin levels. The findings were statistically analyzed using the Pearson correlation test and the comparison tests of averages of independent samples (Student's t).

Patients with PV present high RMI and MFR + HFR (medium and high fluorescence reticulocytes) as compared with secondary polycythemia . We did not find any correlation between RMI and other analytical parameters (erythropoietin, ferritin, serum iron, transferrin), except for the transferrin saturation index (TSI), with a correlation factor r: 0.5486 for p < 0.05.

This higher proportion of younger reticulocytes in PV might be explained because they are a parameter that would reflect the expansion of erythropoietic bone progenitor cells, which would be more increased in PV than in PS. However, another possible explanation would consist in the existence of associated ferropenia in PVs, which lead to an increase in cytoplasmic levels of transferrin receptor mRNA.