Recently, a number of microfluidic methods have been developed for phenotypic separation of leukocytes from small volumes of whole blood. Leukocytes may be separated based on size and deformability using hydrodynamic chromatography, such as deterministic lateral displacement (DLD) or margination. In DLD, cells navigate a 2D array of obstacles along different streamlines based on their distinct size and deformability10–12. Margination relies on preferential migration of leukocytes along a vessel wall and clustering of RBCs in the middle of a vessel, resulting from the hydrodynamic lift generated through the Fåhræus-Lindqvist effect13–16. Alternatively, leukocytes may be separated based on distinct dielectric properties, which arise from cell size as well as nuclear and membrane morphology17, 18, and magnetophoresis, which depletes deoxygenated RBCs based on their specific magnetic susceptibility19–21. A significant challenge for separating leukocytes from whole blood using these approaches is the lack of selectivity both in the depletion of RBCs, as well as in the selectivity for specific phenotypes.