A novel method and a device for assessment of the concentration of advanced glycation end products (AGE), such as pentosidine in particular, in the biological fluids, such as spent dialysate. More specifically, the present invention relates to an optical method utilizing fluorescence and a specific model, including a unique set of optical spectral components at certain wavelengths, to determine, preferable on-line, the concentration of an AGE compound, such as pentosidine.
