An erythrolytic reagent and a leukocyte preservative produce a sample for performing a five-part WBC differential analysis using VCS technology. Reticulocytes are immature erythrocytes (red blood cells) that retain a small amount of RNA as the nucleus is extruded during the maturation process. To detect the presence of this RNA, the red blood cells are stained while they are still viable in a process called supravital staining. Once a whole-blood sample is prepared, reticulocytes are differentiated from mature red blood cells and other cell populations using VCS and reticulocyte counting technologies.