BACKGROUND: Current continuous
glucose monitors have limited
accuracy mainly in the low range of
glucose measurements. This lack of
accuracy is a limiting factor in their clinical use and in the development of the so-called
artificial pancreas. The ability to detect incorrect readings provided by continuous
glucose monitors from raw data and other information supplied by the monitor itself is of utmost clinical importance. In this study,
support vector machines (SVMs), a powerful
statistical learning technique, were used to detect therapeutically incorrect measurements made by the Medtronic MiniMed CGMS((R)). METHODS: Twenty patients were monitored for three days (first day at the hospital and two days at home) using the MiniMed CGMS. After the third day, the monitor data were downloaded to the physician's computer. During the first 12 hours, the patients stayed in the hospital, and
blood samples were taken every 15 minutes for two hours after meals and every 30 minutes otherwise.
Plasma glucose measurements were interpolated using a cubic method for time synchronization with simultaneous MiniMed CGMS measurements every five minutes, obtaining a total of 2281 samples. A Gaussian SVM classifier trained on the monitor's electrical signal and
glucose estimation was tuned and validated using multiple runs of k-fold
cross-validation. The classes considered were
Clarke error grid zones A+B and C+D+E. RESULTS: After ten runs of ten-fold
cross-validation, an
average specificity and sensitivity of 92.74% and 75.49%, respectively, were obtained (see Figure 4). The
average correct rate was 91.67%. CONCLUSIONS: Overall, the SVM performed well, in spite of the somewhat low sensitivity. The classifier was able to detect the time intervals when the monitor's
glucose profile could not be trusted due to incorrect measurements. As a result,
hypoglycemic episodes missed by the monitor were detected.
