Background Recent studies showed that some cell population data (CPD) parameters of neutrophils may be useful for diagnosing myelodysplastic syndromes and sepsis, for the differential diagnosis of acute promyelocytic leukemia, and some CPD parameters of lymphocytes may be a valuable tool for preliminary screening of B cell lymphoproliferative disease. Notwithstanding the knowl edge, no information has been made available about their analytical quality specification. This study was aimed to define short- and medium-term biological variation (BV) estimates and reference change value (RCV) of leukocyte count, extended leukocyte differential and CPD. Methods The study population consisted of 43 healthy volunteers, who participated in the assessment of medium-term (21 volunteers; blood sampling once a week for 5 consecutive weeks) and short-term (22 volunteers; blood sampling once a day for 5 consecutive days) BV, using Sysmex XN. Outlier analysis was carried out before CV-ANOVA, to determine BV estimates and their confidence intervals. Results The medium-term and short-term within-subject BV (CV I ) was comprised between 0.6–19.7% and 0.2–21.9%, whereas the medium-term and short-term between-subjects BV (CV G ) was comprised between 1.2–61.5% and 1.1–58.5%. The RCVs were found to be similar for all the parameters, in both arms of the study, except for some CPD parameters. Conclusion This study allowed accurately estimating the BV of many leukocyte parameters, some of which have not been currently explored. The kinetics of some leukocyte turnover suggests the use of short-term BV data for calculating analytical goals and RCV. © 2017 Elsevier B.V.