A lactate sensor arrangement includes a catheter for withdrawing a test fluid sample, a sensor module for measuring an analyte such as lactate in the sample, and a pumping mechanism. A single uninterrupted flow path extends between the pumping mechanism and the catheter and within the flow path resides a sensor module containing a test chamber. The sensor arrangement also includes a control unit or controller that interfaces with a pumping mechanism driver. The sensor arrangement also includes a source of sensor calibration and anticoagulant solution, such as a reservoir.