An apparatus and method for predicting a parameter in the blood stream of a subject is disclosed. The apparatus includes a laser diode source arranged to emit light of at least two different wavelengths a first optical receiver arranged to receive incident light of the two different wavelengths where the subject is not present a second optical receiver arranged to receive transmitted or diffuse reflected light of the two different wavelengths when a desired part of the subject is present and a processor for calculating the ratio of the intensity of the received transmitted or diffuse reflected light to incident light for each of the at least two different wavelengths to provide an indication of the parameter in the blood stream of the subject. The apparatus and method are particularly suited for measuring HbA1c in an individual.
