A fiber optic sensor device for detecting the presence of a chromophoric compound in a biological fluid is disclosed. The fiber optic sensor device includes at least one fiber optic member having an unclad portion, the fiber optic member having a proximal end and a distal end for transmitting light energy of a determinable wavelength, a light source means for generating light energy of determinable wavelength, said light source means operatively associated with a measuring means such that said light energy passes through said measuring means and said fiber optic member to the biological fluid, and measuring means operatively associated with said fiber optic member and said light source, for measuring the difference between said light energy generated by said light source and light reflected from the distal end of the fiber optic member, wherein the difference is related to the light absorbed by the chromophoric compound and indicative of the concentration of the chromophoric compound present in the biological fluid.