Subcutaneous glucose sensor values closely parallel blood glucose during insulin-induced hypoglycaemia

Aims To assess the accuracy of the Minimed continuous glucose monitoring system (CGMS) in estimating blood glucose concentration during a controlled reduction in blood glucose. Research design and methods We studied nine adolescent diabetics (age 14+/-1.5 years) wearing the CGMS during hyperinsulinaemic hypoglycaemic clamp studies. The glucose values obtained by the CGMS were compared with the venous blood samples taken during the studies and measured at the bedside using a glucose oxidase technique. Results Blood glucose was lowered from euglycaemia to a mean of 2.8 mmol/l over 120 min and maintained at that level for a further 40 min. A total of 429 paired glucose measurements were available for analysis. Analysis using weighted Deming regression and t -tests revealed small differences between the methods, with blood glucose levels slightly higher than interstitial fluid levels. The mean difference across all values was 0.13 mmol/l. The observed difference was greatest at blood glucose values < 3.3 mmol/l. Conclusions This study suggests that during a fall in systemic glucose the subcutaneous glucose sensor provides an accurate reflection of blood glucose. However, a small difference is apparent at blood glucose values < 3.3 mmol/l.