The validation of automated hematology analyzer results by manual slide review (MSR) is currently an inevitable work process in clinical hematology laboratories. The laboratory workload would be optimized if the requirement for MSR could be reduced without compromising patient care. We investigated whether slide-making rates would be different between two hematology analyzers, which were paired with their own automated slide makers/stainers: Sysmex XE-2100 with SP-1000i (Sysmex, Kobe, Japan) and ABX Pentra DX120 with SPS evolution (ABX-Horiba, Montpellier, France). Our data show that the slide-making rates are variable in different hematology analyzers. It also implies that although MSR cannot be fully substituted by modern hematology analyzers, it can be effectively reduced to optimize laboratory workload.