A blood treatment system (100, 136), comprising: a machine (104, 300) comprising one or more pumps (102, 132, 133); a blood circuit (101, 141, 301, 303) in engagement with the one or more pumps (102, 132, 133) and having an inlet line (142, 304) and an outlet line (140, 302) for conveying blood to and from a patient, respectively; at least two pressure sensors (108, 109, 110, 111, 144, 148) in at least one of the inlet line or the outlet line; and a controller configured to control the one or more pumps (102, 132, 133) to convey blood to and from the patient, the controller further configured to use readings of the at least two pressure sensors (108, 109, 110, 111, 144, 148, 504, 506) to determine a change over time in a pressure drop across a flow restriction (107, 146, 510) in the blood circuit (101, 141) and perform a function responsive to the change in the pressure drop, the function comprising at least one of: generating a notification, adjusting a blood flow rate in the blood circuit, outputting an estimation of a condition of the machine or the patient, or outputting data responsive to said estimation, characterized in that the controller is configured to sample the pressure drop at multiple times over a period of time comprising a single treatment or multiple treatments and store data responsive thereto, wherein the change in the pressure drop is determined based on a trend over time of the stored data. a machine (104, 300) comprising one or more pumps (102, 132, 133); a blood circuit (101, 141, 301, 303) in engagement with the one or more pumps (102, 132, 133) and having an inlet line (142, 304) and an outlet line (140, 302) for conveying blood to and from a patient, respectively; at least two pressure sensors (108, 109, 110, 111, 144, 148) in at least one of the inlet line or the outlet line; and a controller configured to control the one or more pumps (102, 132, 133) to convey blood to and from the patient, the controller further configured to use readings of the at least two pressure sensors (108, 109, 110, 111, 144, 148, 504, 506) to determine a change over time in a pressure drop across a flow restriction (107, 146, 510) in the blood circuit (101, 141) and perform a function responsive to the change in the pressure drop, the function comprising at least one of: generating a notification, adjusting a blood flow rate in the blood circuit, outputting an estimation of a condition of the machine or the patient, or outputting data responsive to said estimation, characterized in that the controller is configured to sample the pressure drop at multiple times over a period of time comprising a single treatment or multiple treatments and store data responsive thereto, wherein the change in the pressure drop is determined based on a trend over time of the stored data. generating a notification, adjusting a blood flow rate in the blood circuit, outputting an estimation of a condition of the machine or the patient, or outputting data responsive to said estimation, characterized in that the controller is configured to sample the pressure drop at multiple times over a period of time comprising a single treatment or multiple treatments and store data responsive thereto, wherein the change in the pressure drop is determined based on a trend over time of the stored data.