Adolescents with type 1 diabetes aged 12–18 years with hypoglycemia unawareness attending Princess Margaret Hospital diabetes clinics were invited to participate. Hypoglycemia unawareness score was determined by the use of modified Clarke's questionnaire (8
). This questionnaire has been shown to accurately identify patients with impaired awareness of hypoglycemia for both clinical and research purposes (9
). A score of ≥8 is suggestive of hypoglycemia unawareness. Consent was obtained for all participants.
All subjects underwent a hyperinsulinemic hypoglycemic clamp study at baseline to assess hypoglycemic symptoms and hormonal responses. Subjects were then randomized to either standard therapy (standard group) or to the use of real-time (Medtronic Minimed Paradigm REAL-Time System) CGM (CGM group) for 4 weeks. At the end of the 4-week period, all patients underwent a repeat hypoglycemic clamp study.
Hyperinsulinemic hypoglycemic clamp
During this procedure, the antecubital vein was cannulated for insulin and glucose infusion, and blood was sampled from the contralateral hand vein placed in a box heated to 60°C. Regular insulin (Human Actrapid; Novo Nordisk, Crawley, U.K.) was infused at a constant rate of 80 mU/m2/min. Target plasma glucose levels were achieved by adjusting the rate of infusion of 20% glucose in water. Plasma glucose concentrations were maintained initially at euglycemia (5–6 mmol/l) over a period of 1 h. Following this, blood glucose was lowered over 30 min to a nadir of 2.8 mmo/l. The blood glucose concentration of 2.8 mmol/l was maintained for 40 min for the hypoglycemia phase. Euglycemia was then restored.
For the duration of the clamp procedure, blood glucose was analyzed at the bedside using a glucose oxidase technique (YSI 2300; Yellow Springs Instruments, Yellow Springs, OH). Additional samples of arterialised venous blood were taken to measure plasma insulin, glucagon, epinephrine, norepinephrine, cortisol, and growth hormone concentrations.
Following the first hypoglycemic clamp study, both groups were advised to strictly avoid hypoglycemia with fingerstick testing at least four to six times daily to maintain blood glucose levels between 6 and 10 mmol/l for the 4-week period. In addition, the CGM group wore real-time CGM with subcutaneous sensor with preset low alarms at 6 mmol/l and was advised to institute standard hypoglycemia treatment for blood glucose levels below 6 mmol/l with target blood glucose level of 8 mmol/l.
The CGM group received an an additional 2 h of instructions regarding sensor insertion and usage. Sensors were changed every 3 days.
The major outcome measure was the epinephrine response to hypoglycemia measured during the hypoglycemia clamp study. Plasma epinephrine levels were measured by ELISA (Diagnostika GMBH, Hamburg, Germany) and samples were analyzed in duplicate. The interassay coefficient of variation at 10 pmol/l and 5,460 pmol/l were 2% and 5.5%, respectively.