Stability of peripheral blood lymphocyte count and E-rosette forming lymphocytes in healthy adults

Highly reproducible peripheral blood lymphocyte (PBL) count and percent E-rosette forming lymphocyte (%E-RFL) assays were developed by modifying existing procedures. PBL count assay variation was reduced by using replicate electronic white blood cell (WBC) counting and 2,000 WBC differentials. The %E-RFL assay modifications reduced variation and include the use of: (a) a capillary buffy coat isolation procedure that recovered more than 85% of the PBL without the use of chemical separation media, (b) centrifugation temperatures of 20--22 degrees C, and (c) toluidine blue staining that allowed enumeration of %E-RFL and not E-rosette forming cells, by exclusion of nonlymphoid cells. Day-to-day variation of PBL count and %E-RFL was defined by making serial determinations over a period of months. The data indicate that healthy adults maintain PBL counts and %E-RFL within narrow ranges that are specific for each individual.