A blood treatment apparatus includes: a blood treatment unit, a pair of fluid pumps and a pair of blood pumps. The blood treatment unit is configured to receive untreated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid. The fluid pumps are configured to pass blood treatment fluid through the blood treatment unit. The blood pumps are configured to extract untreated blood from a blood source, pass extracted blood through the blood treatment unit and deliver treated blood to a target vessel. Flow measurement device which determines at least one blood flow parameter reflecting an average flow in relation to the blood treatment unit during a well-defined period of operation of the apparatus, for example while completing one operation cycle. The at least one blood flow parameter is determined based on a difference between (i) a first amount of fresh blood treatment fluid received into the blood treatment unit, and (ii) a second amount of used blood treatment fluid emitted from the blood treatment unit during another well-defined period.