Development of a non-invasive method for measuring the blood glucose level is an urgent necessity, and putting such a method into practical use will enable some of the physical and mental stress that patients with diabetes have to endure to be removed. To realise a non-invasive blood glucose monitor, the gingival crevicular fluid (GCF) was measured. A GCF-collecting device was developed that was designed to be disposable, biocompatible and small enough to be inserted in the gingival crevice for collection of a sub-microlitre sample of GCF. Also, a high-sensitivity glucose testing tape incorporated in the device was developed. Red laser light in a portable optical device measured the colour density of the testing tape. Standard glucose solutions were used to investigate the measurement accuracy of the GCF glucose monitor and showed a correlation coefficient of R = 0.99 (n = 20) between the optical density and the glucose levels. The GCF glucose monitor was evaluated on healthy Swedish and Japanese adults (n = 10) and both GCF glucose levels (GCFLs) and blood glucose levels (BGLs) were measured in conjunction with meal loads. The GCFLs were about 1/10-1/560 lower than the BGLs. No difference in the range of GCFLs between the Swedish and the Japanese subjects was observed. Therefore it was concluded that physique, body mass index and life-style, such as dietary habit, did not significantly influence the GCFLs. Further, the correlation coefficients of all the subjects were 0.70 and 0.88 with each group. It was suggested that GCF could be used as a method of non-invasive blood glucose measurement.

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A minute volume such as a few hundred nano-litres of gingival crevicular fluid (GCF) will evaporate within one minute at room temperature after collection. In order to investigate the feasibility of a method for noninvasive blood glucose measurement using this fluid, a fabricated GCF-collecting device, and the time-course changes of blood and GCF glucose levels in diabetics were evaluated. As a result of improvement in the GCF-collecting device such that the color of a filter paper changed from white to black upon collection of the sample, the completion of the collecting procedure could be visually confirmed. Using this device, we succeeded in collecting 200 nl of GCF within 30 s, despite the fact that GCF is usually secreted at a rate between 2 and 3 microl per tooth per hour. This method could be applicable for collecting small volume of other biological fluids. The time-course changes of blood and GCF glucose levels in ten type 2 diabetic subjects were examined, the correlation coefficient, R, between both glucose levels was 0.878. The result proved to be similar to that for normal healthy subjects in a previous study. A significant time difference between the two glucose levels was not observed. In diabetes period of 4.8 +/- 1.7 years, the influence of the disease on the GCF glucose level was minimal. Furthermore, from the ROC curve analysis, both sensitivity and specificity showed favorable results. It was suggested that the measurement of GCF glucose levels was a promising screening method for diabetics.

In order to realize a noninvasive blood glucose monitor, we monitored the gingival crevicular fluid (GCF). In this paper, the clinical evaluations were performed on not only normal subjects but also diabetic subjects using a GCF-glucose monitor to determine blood glucose levels. Meal load tests were carried out and the time-course changes in blood glucose level and GCF glucose level were measured continuously. A positive correlation of more than 0.9 was found between blood glucose level and GCF glucose level, necessitating the calibration of individual correlations for every subject. Finally, the performance of the GCF-glucose monitor was evaluated using Error Grid Analysis. As the results, significant information for the glucose level decision was obtained not only for normal subjects, but also for diabetic subjects.

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