Identifying antibiotic resistance in blood infections requires separating bacteria from whole blood. A hollow spinning disk rapidly removes suspended red blood cells by leveraging hydrodynamic differences between bacteria and whole blood components in a centrifugal field. Once the red cells are removed, the supernatant plasma which contains bacteria is collected for downstream antibiotic testing. This work improves upon previous work by modifying the disk design to maximize fractional plasma recovery and minimize fractional red cell recovery. V-shaped channels induce plasma flow and increase fractional plasma recovery. Additionally, diluting a blood sample spiked with bacteria prior to spinning it increased the fractional bacteria recovery. A numerical model for red cell sedimentation shows that red cells are removed from solution more rapidly as the blood is diluted. Diluting blood is beneficial but may create too much biological waste. The benefits of diluting are formulated as an optimization problem subject to the end user’s needs.