Abstract: A method and apparatus for conducting blood tests on the blood of critically ill or anemic patients includes surrounding a transparent portion of an IV line with a sensor housing bearing radiation sources located on one side of the IV line and radiation sensors located on the opposite or other side of the IV line. A patient's blood can be drawn into the IV line, whereupon the radiation sources, which may be LEDs, are caused to pass radiation through the blood and onto the sensors. The sensors detect characteristics of the received radiation and produce a signal, which can be interpreted by a monitor to determine characteristics of the blood such as oxygen content, hemoglobin levels, and the like.