The present invention is directed toward a method of measuring a blood parameter and, in particular, a glucose measurement system controlled by a novel controller. In one embodiment, the system has a controller, a pump, flush solution in a first reservoir, IV solution in a second reservoir, a first valve, a second valve, and a plurality of tubing placing the pump, reservoirs, and valves in fluid communication with each other. The system operates by establishing a first state where the first state has the first valve open and second valve closed, closing the first valve, instructing the pump to extract fluid from tubing having IV solution therein, sensing a presence of blood at a first location in the tubing, measuring a blood parameter, instructing the pump to re-infuse the extracted fluid back into the tubing, opening the second valve where the second valve permits flush solution to flow from the first reservoir through tubing, instructing the pump to extract fluid from tubing having flush solution therein, closing the second valve, instructing the pump to re-infuse the extracted fluid having flush solution therein back into the tubing, and opening the first valve.