For the first time, near-infrared spectroscopy (NIRS) has demonstrated a capability to accurately measure glucose levels. The device uses fiber optics to illuminate vascular tissue. A tungsten-halogen light is connected to the fiber optic bundle; this is directed at the subject’s thumb. Glucose has its own special “spectral signature” which can be differentiated from other molecules in the tissue. The device then processes this information (which is both reflected and absorbed by the fiber optic light) using a mathematical algorithm to come up with an accurate plasma glucose level.
Research on the efficacy of near-infrared spectroscopy was conducted by the Diabetes Research Center and the General Clinical Research Center at Albert Einstein College of Medicine in New York. It was reported in the December 1999 issue of Diabetes Care. The 12 test subjects (two type 1s and 10 non-diabetics) were tested when their BG levels were between 50 mg/dl and 115 mg/dl. Their plasma glucose levels were measured at five-minute intervals while they were infused with insulin and a 20% dextrose solution. The results of the device were compared with a current standard, the Beckman Glucose Analyzer. The net result, after over 1,700 measurements in this study, is that NIRS results correlate highly with the Beckman Analyzer. Since results can be significantly affected by the pressure of the probe on the subject’s thumb, a special receptacle was used to control the amount of pressure.
The U.S. Food and Drug Administration has not yet approved NIRS for glucose monitoring; citing a lack of consistently reliable determinations of the plasma glucose level. Previous studies with NIRS collected data from probes which were attached to the ear lobe, finger web, the forearm or the finger cuticle, resulting in inconsistencies in readings. This study should dispel some of those inconsistencies. The special thumb receptacle is believed to overcome some of those variations, which may have been related to differences in pressures in the skin. Before NIRS gains widespread clinical acceptance, future studies will have to consider many other factors. Since reliable data depends upon an accurate reading via the skin, more information needs to be compiled with respect to percentage of body fat, skin color, gender, temperature and hydration levels. The results of future studies will have to be confirmed outside of the research lab and within the realm of daily diabetes management.