[Counting reticulocytes: new importance of an old method]

In clinical practice, the reticulocyte count is the most useful method to estimate red cell life span and red cell production. However, experience of hematologists as well as surveys have shown that counting of reticulocytes is often neglected in the diagnostic work-up of unclassified anemias, and many physicians have difficulties in interpreting the results. Formerly, this was partly due to the low precision of manual counts. Today, this method is largely replaced by flow cytometry, available in almost all larger systems for automated blood count analysis, at low costs and sufficient analytic precision. Interpretation is supported by calculated parameters such as the Reticulocyte Production Index. Here, the authors discuss the limits of the analytic methods and the problems of interpretation in the context of the laboratory profile and the clinical setting.