A blood processing apparatus (1) comprises a measurement device (8) having a first chamber element (80) for measuring a haematocrit value of a blood fluid, the first chamber element (80) comprising a first inlet port (800) connectable to a first reservoir container (2) for allowing a flow from the first reservoir container (2) into the first chamber element (80) and a first outlet port (801) for allowing a flow out of the first chamber element (80), and the second chamber element (81) comprising a second inlet port (810) for allowing a flow into the second chamber element (81) and a second outlet port (811) connectable to a second reservoir container (3) for allowing a flow out of the second chamber element (81) towards the second reservoir container (3). The blood processing apparatus furthermore comprises a first pump mechanism (600) for pumping a blood fluid in a flow direction (F1) from the first reservoir container (2) towards the blood processing apparatus (1), and a second pump mechanism (610) for pumping a blood fluid in a flow direction (F2) from the blood processing apparatus (1) towards the second reservoir container (2). Herein, the first pump mechanism (600) is located upstream of the first inlet port (800) of the first chamber element (80) and the second pump mechanism (610) is located upstream of the second inlet port (810) of the second chamber element (81). In this way a blood processing apparatus comprising a measurement device is provided which in an easy and reliable manner allows for a measurement of in particular a haematocrit value in the incoming blood flow as well as the outgoing blood flow.L'invention concerne un appareil de traitement du sang (1) comprenant un dispositif de mesure (8) ayant un premier élément de chambre (80) pour mesurer une valeur d'hématocrite d'un fluide sanguin, le premier élément de chambre (80) comprenant un premier orifice d'entrée (800) pouvant être connecté à un premier conteneur réservoir (2) pour permettre un éc
