OBJECTIVE: To evaluate the accuracy of nocturnal continuous glucose monitoring by CGMS. RESEARCH DESIGN AND METHODS: A CGMS was inserted in 14 type 2 diabetic patients on combined oral and insulin therapy at altogether 15 occasions. During the second (48 hours) and third (72 hours) night of registration each subject was observed and plasma glucose was analysed seven times during the night by venous sampling and compared to CGMS. These venous values were not used for calibration of the sensor. Pairs of data were analysed using correlation coefficient, Bland-Altman graphs and Clarke Error Grid analysis. RESULTS: 32% of CGMS data did not meet the quality criteria for optimal accuracy and were excluded. A correlation coefficient of 0.80 (p < 0.0001) was seen after 48 hours and a lower coefficient of 0.33 (p = 0.0082) after 72 hours. Bland-Altman analyses demonstrated that the dispersion of the values around the mean of differences was wider after 72 hours as compared to after 48 hours. In the Clark Error Grid analysis 100% of data were within zones A and B after 48 hours, with 60% in zone A. After 72 hours only 44% were in zone A and 7% of data were in the clinically unacceptable zone D. CONCLUSION: The MiniMed Medtronic CGMS has acceptable nocturnal accuracy after 48 hours of registration, but the accuracy thereafter deteriorates with time, implicating that the CGMS thereafter may prove less useful for nocturnal monitoring.
OBJECTIVE: To evaluate the accuracy of nocturnal continuous glucose monitoring by CGMS. RESEARCH DESIGN AND METHODS: A CGMS was inserted in 14 type 2 diabeticpatients on combined oral and insulin therapy at altogether 15 occasions. During the second (48 hours) and third (72 hours) night of registration each subject was observed and plasma glucose was analysed seven times during the night by venous sampling and compared to CGMS. These venous values were not used for calibration of the sensor. Pairs of data were analysed using correlation coefficient, Bland-Altman graphs and Clarke Error Grid analysis. RESULTS: 32% of CGMS data did not meet the quality criteria for optimal accuracy and were excluded. A correlation coefficient of 0.80 (p < 0.0001) was seen after 48 hours and a lower coefficient of 0.33 (p = 0.0082) after 72 hours. Bland-Altman analyses demonstrated that the dispersion of the values around the mean of differences was wider after 72 hours as compared to after 48 hours. In the Clark Error Grid analysis 100% of data were within zones A and B after 48 hours, with 60% in zone A. After 72 hours only 44% were in zone A and 7% of data were in the clinically unacceptable zone D. CONCLUSION: The MiniMed Medtronic CGMS has acceptable nocturnal accuracy after 48 hours of registration, but the accuracy thereafter deteriorates with time, implicating that the CGMS thereafter may prove less useful for nocturnal monitoring.