An extracorporeal blood processing system which includes a disposable assembly. The system includes a disposable assembly that has integral fluid passageways. A blood removal conduit and a blood return conduit are interconnected with the integral fluid passageways. A diaphragm is mounted in the disposable assembly and is removably attachable to a sensor via a number of alternative connection devices. In one embodiment, the sensor may include a transducer that is capable of measuring the force exerted on the diaphragm. The corresponding force may be correlated to a pressure of fluid in either the blood removal conduit and/or the blood return conduit.