Comparison of the Automated Reticulocyte Counts and Immature Reticulocyte Fraction Measurements Obtained With the ABX Pentra 120 Retic Blood Analyzer and the Sysmex XE-2100 Automated Hematology Analyzer

Carol Briggs, Donna Grant, Samuel J. Machin

Automated counting of reticulocytes has greatly increased the precision and accuracy of this assay compared with traditional manual counts. In addition, reticulocyte maturity can now be assessed based on the staining intensity of the reticulocytes, which is proportional to their RNA content. Newly produced or immature reticulocytes may be defined by a relatively high degree of RNA staining, whereas more mature forms show less staining. This difference in staining makes possible the identification of the youngest highly fluorescent reticulocytes prematurely delivered into the circulation from the bone marrow in conditions of increased erythropoietic stimulation or during regeneration of erythropoietic activity in patients receiving bone marrow or stem cell transplants. We evaluated reticulocyte counting and measurement of the immature reticulocyte fraction (IRF) with the ABX Pentra 120 Retic blood analyzer (Montpellier, France) using over 300 blood samples. Results were compared with those obtained from the Sysmex XE-2100 Automated Hematology analyzer (Sysmex Corporation, Kobe, Japan). Comparison of the 2 methods showed excellent correlation for reticulocyte percentage and absolute count (Pearson product moment [r] = 0.95 for both parameters). There was also good correlation between the IRF expressed by the ABX Pentra 120 Retic and the Sysmex XE-2100 (r = 0.77), although the ABX Pentra gave significantly higher values than did the XE-2100. This difference in values is a result of methodological differences in deriving the IRF measurements, ie, the influence of both the fluorescent stain used and the software thresholds for the IRF. Because the IRF has now been proven to be a useful clinical parameter, there needs to be some standardization and calibration of IRF methods.

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