CLINICAL-SIGNIFICANCE OF IMMATURE RETICULOCYTE FRACTION DETERMINED BYAUTOMATED RETICULOCYTE COUNTING

The Sysmex R-3000 (TOA Medical Electronics, Kobe, Japan) evaluates mat uration of reticulocytes by quantitating the fraction of reticulocytes within low-, middle-, and high-fluorescence intensity regions. We def ined the immature reticulocyte fraction (IRF) as the sum of the fracti on of high-fluorescence intensity regions plus the fraction of middle- fluorescence intensity regions. Then, we studied the clinical signific ance of IRF in the evaluation of anemia by comparing the IRF with the absolute reticulocyte count (ARC) and with the reticulocyte production index (RPI) and by reviewing pertinent clinical information about the patients. In the study, 132 specimens from 102 patients undergoing ev aluation of anemia were analyzed. By using simple regression analysis, our results showed that the IRF has a weak but significantly positive correlation with ARC and with RPI, indicating that IRF is an addition al useful parameter to evaluate the erythropoietic activity in anemia. Interpretation by integrating IRF and reticulocyte enumeration (ARC a nd RPI) provided useful information for further subclassification of a nemia. Increased IRF (IRF greater than or equal to 0.23) and increased ARC generally indicated an adequate erythroid response to anemia. All but three specimens with an IRF less than 0.23 showed an RPI of 2 or less. These specimens were from patients with underlying diseases know n to lead to decreased erythropoietic activity, predominantly chronic renal insufficiency. Specimens with a subnormal or normal ARC (with a corresponding RPI less than or equal to 2) but with an IRF of more tha n 0.23 were from patients with various underlying conditions, includin g acute infection, iron deficiency anemia, human immunodeficiency Viru s infection, sickle disease with crisis, pregnancy, and myelodysplasti c syndrome. Our results indicate that an IRF of 0.23 or less in patien ts with anemia reflects bone marrow that is nonresponsive or underresp onsive to the anemia. Patients with an increased IRF (IRF greater than or equal to 0.23) may require further examination to clarify the caus e of the anemia.