Mixed-Meal Tolerance Test Versus Glucagon Stimulation Test for the Assessment of β-Cell Function in Therapeutic Trials in Type 1 Diabetes

Clinical Care/Education/Nutrition/Psychosocial Research

Carla J. Greenbaum, MD,
Thomas Mandrup-Poulsen, MD, PHD,
Paula Friedenberg McGee, MS,
Tadej Battelino, MD, PHD,
Burkhard Haastert, PHD,
Johnny Ludvigsson, MD, PHD,
Paolo Pozzilli, MD, PHD,
John M. Lachin, SCD,
Hubert Kolb, MD, PHD and
The Type 1 Diabetes Trial Net Research Group and the European C-Peptide Trial Study Group*

Diabetes Care 2008 Oct; 31(10): 1966-1971. https://doi.org/10.2337/dc07-2451

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Figure 1—
TrialNet mean peak C-peptide (solid lines) and 95% CI bands (dotted lines), from an MMTT (upper solid lines) and a GST (lower solid lines) with respect to the age of onset in subjects with duration of type 1 diabetes <1 year (A), 1–2 years (B), and 2–3 years (C) obtained from separate models within each duration category with an interaction between test (MMTT versus GST) and age at onset of type 1 diabetes, adjusted for fasting C-peptide, fasting glucose, weight, visit number, and randomization group.
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Figure 2—
Relationship between the duplicate measurements of the peak (A) and AUC mean C-peptide values (B) (pmol/ml) from the MMTT and the GST. The 6-min European GST values are presented in lieu of the peak values.

Table 1—

Baseline characteristics of the TrialNet and ECPT participants

	TrialNet	ECPT	Combined data*
n	148	118	230
Male sex (%)	91 (61)	70 (59)	138 (60)
Age (years)
Median (range)	15 (8–35)	19 (8–40)	16 (8–35)
Means ± SD	16.2 (6.19)	20.3 (7.54)	17.2 (6.53)
Categories
8–12 years (%)	51 (34)	26 (22)	73 (32)
13–17 years (%)	49 (33)	26 (22)	66 (29)
≥18 years (%)	48 (32)	66 (56)	91 (40)
Race
White	128 (86)	116 (98)	208 (90)
African American	6 (4)	0 (0)	6 (3)
American Indian	3 (1)	0 (0)	3 (1)
Asian	4 (3)	1 (0.85)	5 (2)
Other	7 (5)	1 (0.85)	8 (3)
Ethnicity
% Hispanic	10 (7)	N/A	N/A
Duration of type 1 diabetes (years)
Median (range)	1.36 (0.08–2.98)	2.32 (0.75–4.97)	1.49 (0.08–2.98)
Mean ± SD	1.4 ± 0.88	2.5 ± 1.27	1.54 ± 0.84
Categories
0 to <1 year	60 (41)	15 (13)	75 (33)
1 to <2 years	39 (26)	34 (29)	72 (31)
2 to <3 years	49 (33)	34 (29)	83 (36)
3 to <4 years	N/A	14 (12)	N/A
4 to <5 years	N/A	21 (18)	N/A
A1C (%)	7.3 ± 1.4

Data are n (%), median (range), and means ± SD.
↵* Restricted to TrialNet and ECPT study subjects with diabetes duration of 3 months to 3 years and 8–35 years of age. N/A, not applicable.

Table 2—

Fasting and stimulated C-peptide concentrations

Data are geometric means (95% CI). Geometric means, calculated as exp[mean log(x)], are from a mixed-model analysis of the log(C-peptide) adjusted for fasting glucose concentration, age, sex, continuous diabetes duration, test order, and sequence group. Analyses of stimulated values were also adjusted for basal log(C-peptide). Analyses were conducted separately for TrialNet and EPCT.
↵* P < 0.0001 for the comparison between the TrialNet GST and MMTT. N/A, not applicable.