Erythrokinetics: Evaluation of Red Cell Production by Ferrokinetics and Reticulocyte Counts

Abstract. Effective erythroid marrow activity was quantitated by reticulocyte counts and iron kinetics in normal individuals and in 50 patients suffering from various haematological disorders. To allow direct comparison between both measurements normal base line values were established and defined as production index 1. The erythrocyte iron turnovers as calculated from plasma iron turnover and radioiron red cell incorporation were divided by the figure found in normal subjects, 0.49 mg per 100 ml whole blood per day. Reticulocyte percentages were first corrected for changing haematocrit levels considering as normal 1 and 45% respectively. In this form reticulocyte counts overestimated effective red cell production in the majority of anaemic patients. Further correction was needed to account for the well known inverse temporal relationship between the erythropoietin-induced marrow transit acceleration and the prolonged maturation period of circulating reticulocytes. For this purpose the haematocrit-corrected reticulocyte counts were divided by the fraction marrow transit time normal (3.5 days)/marrow transit time patient. This parameter is defined as the time period necessary for 50% appearance of maximum cellular activity. Now production indices derived from the 2 methods agreed almost perfectly. Marrow transit times were related to characteristics of the peripheral blood film, i.e. polychromasia and mean morphological reticulocyte maturation stage. On this basis guidelines were worked out for a meaningful interpretation of reticulocyte counts.