A catheter-based medical device includes a catheter that is configured and arranged for at least partial insertion into a patient and that defines at least one lumen that is configured and arranged to receive a first fluid. A conductive-fluid detector is coupled to the at least one lumen and is configured and arranged to detect when a second fluid is disposed within the at least one lumen that is more conductive than the first fluid. The conductive-fluid detector includes a plurality of axially-positioned bodies, each body defining a lumen. The lumens of the axially-positioned bodies are aligned to form a shared lumen in fluid communication with the at least one lumen of the catheter. Spaced apart electrodes are disposed within the shared lumen.
