title: Accuracy of continuous glucose monitoring during exercise in type 1 diabetes pregnancy.
abstract: 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.
  
  
  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(®) 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.
authors: University of Cambridge Metabolic Research Laboratories and National Institute for Health Research Cambridge Biomedical Research Centre, Cambridge, United Kingdom. kk426@medschl.cam.ac.uk
authors: Kavita
authors: K
authors: Kumareswaran
authors: Daniela
authors: D
authors: Elleri
authors: Janet M
authors: JM
authors: Allen
authors: Karen
authors: K
authors: Caldwell
authors: Marianna
authors: M
authors: Nodale
authors: Malgorzata E
authors: ME
authors: Wilinska
authors: Stephanie A
authors: SA
authors: Amiel
authors: Roman
authors: R
authors: Hovorka
authors: Helen R
authors: HR
authors: Murphy
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D015190:Blood Glucose Self-Monitoring / Q000379:methods*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000188:drug therapy*; D005080:Exercise Test; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage; D007328:Insulin / Q000008:administration & dosage; D007332:Insulin Infusion Systems; D018670:Monitoring, Ambulatory; D009043:Motor Activity; D011247:Pregnancy; D011254:Pregnancy in Diabetics / Q000097:blood / Q000188:drug therapy*; D015203:Reproducibility of Results; D057185:Sedentary Behavior; D006113:United Kingdom
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin; D007004:Hypoglycemic Agents; D007328:Insulin; C517652:hemoglobin A1c protein, human