White blood cell (WBC) counts and their subgroups of cell types such as neutrophils, lymphocytes, monocytes, eosinophils and basophils (often called differentials), are common clinical measurement to diagnose and monitor a variety of pathologic conditions such as bacterial or viral infections, inflammation, leukemia, immunodeficiency states, and post-chemotherapy, or as part of a complete blood cell count in a routine health checkup. WBC counts and differentials are currently performed in central laboratories using blood analyzers with blood collected by venipuncture. Point of care (POC) analyses of complete blood cell counts are being developed with the aim to reduce turnaround time and increase the chance that more timely medical decisions can be made in remote sites, or in outpatient settings. Currently, four POC WBC systems are being used: Chempaq XBC (Chempaq A/S, Denmark), HemoCue WBC (HemoCue AB, Angelholm, Sweden), pocH -100i (Sysmex Corporation, Kobe, Japan), and ABX-MicrosCRP200 (Horiba Medical, Montpellier, France). The HemoCue, pocH-100i and ABX-MicrosCRP200 systems are available for use in Canada. This Rapid Response review aims to compare the clinical effectiveness, accuracy, precision, and cost-effectiveness of POC testing technologies to assess WBC counts and differentials compared to central laboratory methods. Guidelines associated with the use of POC testing to assess WBC count and differentials will also be examined.