Journal
DIABETES TECHNOLOGY & THERAPEUTICS
Volume 15, Issue 3, Pages 223-229Publisher
MARY ANN LIEBERT, INC
DOI: 10.1089/dia.2012.0292
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Funding
- Diabetes UK [BDA 07/003551]
- Juvenile Diabetes Research Foundation
- Abbott Diabetes Care (Freestyle Navigator CGM and sensors)
- Investigator-Initiated Study Program of Animas Corporation (Animas 2020(R) insulin pump)
- Medical Research Council Centre for Obesity and Related Metabolic Diseases
- National Institute for Health Research Cambridge Biomedical Research Centre
- Addenbrooke's Clinical Research Facility (Cambridge, United Kingdom)
- Medtronic
- Roche
- Novo Nordisk
- Eli Lilly
- Becton Dickinson
- MRC [G0600717] Funding Source: UKRI
- Diabetes UK [07/0003551] Funding Source: researchfish
- Medical Research Council [G0600717, G0600717B] Funding Source: researchfish
- National Institute for Health Research [CDF-2013-06-035, PDF/01/036] Funding Source: researchfish
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Background: Performance of continuous glucose monitors (CGMs) may be lower when glucose levels are changing rapidly, such as occurs during physical activity. Our aim was to evaluate accuracy of a current-generation CGM during moderate-intensity exercise in type 1 diabetes (T1D) pregnancy. Subjects and Methods: As part of a study of 24-h closed-loop insulin delivery in 12 women with T1D (disease duration, 17.6 years; glycosylated hemoglobin, 6.4%) during pregnancy (gestation, 21 weeks), we evaluated the Freestyle Navigator (R) sensor (Abbott Diabetes Care, Alameda, CA) during afternoon (15:00-18:00 h) and morning (09:30-12:30 h) exercise (55 min of brisk walking on a treadmill followed by a 2-h recovery), compared with sedentary conditions (18:00-09:00 h). Plasma (reference) glucose, measured at regular 15-30-min intervals with the YSI Ltd. (Fleet, United Kingdom) model YSI 2300 analyzer, was used to assess CGM performance. Results: Sensor accuracy, as indicated by the larger relative absolute difference (RAD) between paired sensor and reference glucose values, was lower during exercise compared with rest (median RAD, 11.8% vs. 18.4%; P < 0.001). These differences remained significant when correcting for plasma glucose relative rate of change (P < 0.001). Analysis by glucose range showed lower accuracy during hypoglycemia for both sedentary (median RAD, 24.4%) and exercise (median RAD, 32.1%) conditions. Using Clarke error grid analysis, 96% of CGM values were clinically safe under resting conditions compared with only 87% during exercise. Conclusions: Compared with sedentary conditions, accuracy of the Freestyle Navigator CGM was lower during moderate-intensity exercise in pregnant women with T1D. This difference was particularly marked in hypoglycemia and could not be solely explained by the glucose rate of change associated with physical activity.
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