Apparatus for extracorporeal blood treatment, comprising a blood treatment unit that comprises at least one compartment , a first blood line that is connected to a connection of the compartment and comprises a first patient connection , a second blood line that is connected to a connection of the compartment and comprises a second patient connection , a blood pump for conveying blood, a device for measuring a physical or chemical characteristic variable, a control and evaluation unit that is connected to the blood pump and to the device for measuring a physical or chemical characteristic variable, and is designed such that the blood pump can be operated in a first operating mode having a normal blood flow, such that blood flows from the first patient connection to the blood treatment unit and from the blood treatment unit to the second patient connection , the blood pump can be operated in a second operating mode having a reversed blood flow, such that blood flows from the second patient connection to the blood treatment unit and from the blood treatment unit to the first patient connection , and the haemodynamic parameter is determined from the measured physical or chemical characteristic variable during normal and reversed blood flow, characterised in that an apparatus for collecting blood clots is provided at least in the first blood line , the apparatus for collecting blood clots comprising a housing body having a first connection and a second connection , and a screen body for catching the blood clots that is arranged between the two connections in the flow path of the blood, the apparatus for collecting blood clots being designed such that a flow path bypassing the screen body forms in the housing body when blood flows in at the second connection and out at the first connection, and a flow path bypassing the screen body does not form when blood flows in at the first connection and out at the second connection. a blood treatment unit that comprises at least one compartment , a first blood line that is connected to a connection of the compartment and comprises a first patient connection , a second blood line that is connected to a connection of the compartment and comprises a second patient connection , a blood pump for conveying blood, a device for measuring a physical or chemical characteristic variable, a control and evaluation unit that is connected to the blood pump and to the device for measuring a physical or chemical characteristic variable, and is designed such that the blood pump can be operated in a first operating mode having a normal blood flow, such that blood flows from the first patient connection to the blood treatment unit and from the blood treatment unit to the second patient connection , the blood pump can be operated in a second operating mode having a reversed blood flow, such that blood flows from the second patient connection to the blood treatment unit and from the blood treatment unit to the first patient connection , and the haemodynamic parameter is determined from the measured physical or chemical characteristic variable during normal and reversed blood flow, characterised in that an apparatus for collecting blood clots is provided at least in the first blood line , the apparatus for collecting blood clots comprising a housing body having a first connection and a second connection , and a screen body for catching the blood clots that is arranged between the two connections in the flow path of the blood, the apparatus for collecting blood clots being designed such that a flow path bypassing the screen body forms in the housing body when blood flows in at the second connection and out at the first connection, and a flow path bypassing the screen body does not form when blood flows in at the first connection and out at the second connection. <EOS>