Insulin, Long-Acting

Details about study design and laboratory and statistical methods are provided in an online appendix (available at http://dx.doi.org/10.2337/dc07-2451).
TrialNet enrolled 148 subjects between September 2004 and December 2005 at 14 clinical centers in North America, 1 in Europe, and 1 in Australia. The ECPT enrolled 118 subjects between April 2004 and December 2004 in 12 European centers. Institutional or ethics board approval was obtained at each site, and each subject or parent, as appropriate, provided informed consent and/or assent. Type 1 diabetes was diagnosed by American Diabetes Association criteria within the past 1 month to 3 years (TrialNet) or by the World Health Organization 1999 criteria within 4 years (ECPT). Patients being treated with drugs that influence β-cell function or influence insulin sensitivity were excluded.
TrialNet randomly allocated subjects 8–35 years of age to receive either two MMTTs followed by two GSTs or the opposite sequence 3–10 days apart. ECPT randomly allocated subjects to receive two MMTTs or GSTs followed by one GST or MMTT. Subjects were stratified by age (8–17 vs. 18–35 years) and duration of diabetes (1 year ± 3 months, 2 years ± 6 months, or 4 years ± 12 months) with approximately equal numbers within each stratum. The latter two duration subgroups were randomly allocated together.
The MMTTs and GSTs were initiated before 10 a.m. Subjects receiving a continuous subcutaneous insulin infusion (insulin pump) could continue to use the usual basal rate. Subjects were instructed to withhold long-acting insulin on the morning of the test. TrialNet allowed use of rapid-acting insulin by injection or continuous subcutaneous insulin infusion up to 2 h before the test and short-acting insulin up to 6 h before the test. ECPT subjects withheld rapid or short-acting insulin for 6 h before the test. Tests were rescheduled if the subject had a capillary glucose value >200 mg/dl or <70 mg/dl. C-peptide concentrations are presented as picomoles per milliliter.

Twenty-four obese adolescents with NGT, 13 with IFG, 29 with IGT, 11 with combined IFG/IGT, and 30 with type 2 diabetes (African American n = 45 and American white n = 62) adolescents were studied. IFG was defined according to the 2003 American Diabetes Association (ADA) guidelines as fasting plasma glucose (FPG) of ≥100–125 mg/dl (13 (link)), based on the average of two fasting glucose measurements at the time of the OGTT (at −15 and 0 min) or the average of seven fasting glucose measurements obtained during the two clamp procedures (three samples every 15 min at the baseline of the hyperglycemic clamp and four samples every 10 min at the baseline of the euglycemic clamp) and NGT with 2-h post-OGTT glucose of <140 mg/dl. IGT was defined as normal FPG <100 mg/dl and 2-h post-OGTT glucose of ≥140–199 mg/dl according to ADA criteria (13 (link)). Those with combined IFG/IGT had FPG ≥100–125 mg/dl and 2-h glucose between ≥140 and 199 mg/dl (13 (link)). All subjects were pubertal and had exogenous obesity with no clinical evidence of endocrinopathy associated with obesity. They were not involved in any regular physical activity or weight reduction programs. Type 2 diabetes in the adolescents was clinically diagnosed according to ADA and World Health Organization criteria (14 (link)). Type 2 diabetic adolescents were negative for GAD and insulinoma-associated protein-2 autoantibody. They were being treated with lifestyle alone (n = 7), metformin (n = 11), metformin + insulin (n = 10), or insulin alone (n = 2). All other participants were not taking any medications that affect glucose metabolism. In type 2 diabetic subjects, metformin and long-acting insulin were discontinued 48 h before the clamp studies. Some of the participants (12 with NGT, 19 with IGT, and 17 with type 2 diabetes) have been reported before (12 (link)). All studies were approved by the institutional review board of the University of Pittsburgh. Informed consent was obtained. Clinical characteristics of the study subjects are summarized in Table 1.

A total of 12 obese adolescents with NGT, 19 with IGT, and 17 with type 2 diabetes were studied; subjects were African-American and American Caucasian. All subjects had exogenous obesity and were not involved in any regular physical activity or weight-reduction programs. They were recruited through flyers posted in the community and the health center. The NGT and IGT adolescents had normal fasting glucose (<100 mg/dl), with a 2-h glucose value during an oral glucose tolerance test (OGTT) of <140 mg/dl in NGT and 140–199 mg/dl in IGT subjects. They were not on any medications that affect glucose metabolism. The adolescents with type 2 diabetes were clinically diagnosed according to American Diabetes Association and World Health Organization criteria (10 (link)), with a mean A1C of 10.1 ± 3.0% and glucose level of 277.2 ± 158.2 mg/dl at presentation and negative glutamic acid decarboxylase and islet cell autoantibodies. They all had adequate metabolic control, with an average A1C of 6.6 ± 0.2% (range 4.7–8.3%) and average duration of diabetes of 4.8 ± 5.7 months (0–18 months). They were on treatment consisting of lifestyle changes alone (n = 3), metformin (n = 6), metformin + insulin (n = 7), or insulin alone (n = 1). Metformin and long-acting insulin were discontinued 48 h before the clamp studies. All studies were approved by the institutional review board of the University of Pittsburgh. Informed consent was obtained. Characteristics of the study participants are summarized in Table 1.