A system for monitoring glucose blood level of a user is disclosed. The system comprising an illumination unit configured for providing coherent optical illumination on a selected inspection region on the user body, a collection unit configured for collecting light returning from the inspection region and generating a plurality of image data pieces associated with speckle patterns in the collected light, and a control unit comprising a processing utility and storage utility comprising pre-stored calibration data, the processing utility is configured for receiving input data on a plurality of image data pieces from the collection unit and for processing said input data for determining correlation functions between different image data pieces and using said correlation functions and said pre-stored calibration data for determining data on glucose blood level of the user.