Non-invasive monitoring of metabolites using near infrared spectroscopy: state of the art.

Non-invasive instrumentation for metabolite monitoring can be based on near-infrared spectroscopy. The main research emphasis is on the development of glucose assays, which could be used for patient self-monitoring. Some histological and physiological variability during in-vivo measurements with integral tissue probing is discussed. The state of non-invasive monitoring is presented and compared with other competing methodologies. Different techniques have been proposed so far, which include transmission and diffuse reflectance measurements. Other methods employ photoacoustic laser spectroscopy or the measurement of changes in radiation scattering due to variations in glucose concentration. Currently available technology requires further improvements, in particular for the normal and hypoglycemic ranges, if it is to be used for devices for self- and bedside-monitoring or during surgery. The necessary selectivity for reliable glucose concentration prediction may only be gained by multivariate data analysis exploiting information from broad spectral ranges because of overlapping spectral features from several other biocomponents in the body tissue under investigation.