Processing systems and methods comprise a separation device that, in use, performs a separation process including separation of red blood cells from blood or a suspension containing red blood cells. The systems and methods include an outlet line coupled to the separation device to remove red blood cells from the separation device, at least in part, while the separation process occurs. A sensor associated with the outlet line senses hematocrit of red blood cells removed from the separation device and generates a sensed hematocrit output. A controller is coupled to the separation device to control removal of red blood cells from the separation device based, at least in part, upon the sensed hematocrit output.