A method of determining a measure of a tissue state (e.g., glycation end-product or disease state) in an individual. A portion of the tissue of the individual is illuminated with excitation light, then light emitted by the tissue due to fluorescence of a chemical with the tissue responsive to the excitation light is detected. The detected light can be combined with a model relating fluorescence with a measure of tissue state to determine a tissue state. The invention can comprise various light excitation and detection configurations. The invention also can comprise correction techniques that reduce determination errors due to detection of light other than that from fluorescence of a chemical in the tissue. Other biologic information can be used in combination with the fluorescence properties to aid in the determination of a measure of tissue state. The invention also comprises apparatuses suitable for carrying out the method.