(A) Image processing algorithm for evaluating capillary flow velocities from smartphone-acquired videos: (1) Parsed 30 fps video to 1 s image shots; (2) Color balanced image to [150, 100, 100] RGB pixel intensities; (3) Extracted green channel image with user-designated channel crop tool; (4) Cropped, binary, and inverted images of channel of interest, from left to right. (B) Capillary flow velocities in relation to dosed buffy coat with cell concentration from 0 to 102 cells/μL at four different time intervals: Δt1, Δt2, Δt3, and Δt4, which correlated to 2 to 6 s, 7 to 12 s, 13 to 22 s, and 23 to 32 s, respectively.