Evaluation of measurement sites for noninvasive blood glucose sensing withnear-infrared transmission spectroscopy

Six putative measurement sites were evaluated for noninvasive sensing of bl ood glucose by first-overtone near-infrared spectroscopy. The cheek, lower lip, upper lip, nasal septum, tongue, and webbing tissue between the thumb and forefinger were examined. These sites were evaluated on the basis of th eir chemical and physical properties as they pertain to the noninvasive mea surement of glucose. Critical features included the effective optical pathl ength of aqueous material within the tissue and the percentage of body fat within the optical path. Aqueous optical paths of 5 mm are required to meas ure clinically relevant concentrations of glucose in the first-overtone reg ion. All of the tested sites met this requirement. The percentage of body f at affects the signal-to-noise ratio of the measurement and must be minimiz ed for reliable glucose sensing. The webbing tissue contains a considerable amount of fat tissue and is clearly the worse;measurement site. All other sites possess substantially less fat, with the least amount of fat in tongu e tissue. For this reason, the tongue provides spectra with the highest sig nal-to-noise ratio and is, therefore, the site of choice on the basis of sp ectral quality. (C) 1999 American Association for Clinical Chemistry.