F reticulocytes assay: A method to evaluate fetal hemoglobin production

Production of fetal hemoglobin (Hb F) involves molecular as well as cellula r aspects as, among red blood cells, it is restricted to a specific populat ion referred as the F cells. Thus understanding the mechanisms involved in persistence or reemergence of Hb F production in various inherited or acqui red conditions requires the measurement of both Hb F and F cells. In additi on, in disorders with a hemolytic component, including sickle cell disease (SCD), because of a probable preferential survival of F cells as compared t o non-F cells, the true parameter off cell production is the F reticulocyte count. The F cells/F reticulocytes ratio then selectively reflects this pr eferential survival. Here we describe an original immunofluorescence micros copy assay that permits the simultaneous measurement of F cells and F retic ulocytes. For this assay to be widely usable, we chose to use commercially available monoclonal antibodies.