The application of lab-on-a-chip systems to biomedical engineering and medical biology is rapidly growing. Reciprocating micropumps show significant promise as automated bio-fluid handling systems and as active reagent-to-sample mixers. Here, we describe a thorough fluid dynamic analysis of an active micro-pump-mixer designed for applications of preclinical blood analysis and clinical diagnostics in hematology. Using high-speed flow visualization and micro-particle image velocimetry measurements, a parametric study is performed to investigate the fluid dynamics of six discrete modes of micropump operation. With this approach, we identify an actuation regime that results in optimal sample flow rates while concomitantly maximizing reagent-to-sample mixing.