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. 2012 Jun;166(6):1021-9.
doi: 10.1530/EJE-11-0797. Epub 2012 Mar 21.

Levels of C-peptide, body mass index and age, and their usefulness in classification of diabetes in relation to autoimmunity, in adults with newly diagnosed diabetes in Kronoberg, Sweden

Maria Thunander  1 , Carina Törn, Christer Petersson, Birger Ossiansson, Jan Fornander, Mona Landin-Olsson
Affiliations

Levels of C-peptide, body mass index and age, and their usefulness in classification of diabetes in relation to autoimmunity, in adults with newly diagnosed diabetes in Kronoberg, Sweden

Maria Thunander et al. Eur J Endocrinol. 2012 Jun.

Abstract

Objective: C-peptide is a main outcome measure in treatment trials of diabetes. C-peptide also has a role in the classification of diabetes, which is often difficult in adults and this is also increasingly recognised in adolescents and elders.

Aim: We aimed to describe the levels of C-peptide in relation to age and body mass index (BMI) in a large population-based cohort of adults with newly diagnosed diabetes and compare the capabilities of C-peptide, age and BMI to discriminate between autoimmune and non-autoimmune diabetes.

Subjects and methods: Blood samples from 1180 patients were analysed regarding islet cell antibody, glutamic acid decarboxylase antibody and fasting C-peptide (FCP). Receiver operating characteristics (ROC) curves were analysed to check the ability of age, BMI and C-peptide to discriminate between autoantibody-positive (Ab(+)) and -negative (Ab(-)) diabetes.

Results: Mean FCP was 0.73±0.5 (range 0.13-1.80) nmol/l in the Ab(+) and 1.42±0.9 (range 0.13-8.30) nmol/l in the Ab(-). FCP was 0.02 nmol/l higher per year increase in age at diagnosis of diabetes. Mean BMI was 26.0±4.8 (range 18.0-39.0) kg/m(2) in the Ab(+) and 28.9±5.3 (range 15.5-62.6) kg/m(2) in the Ab(-). FCP increased with age also within each BMI group. The highest area under the curve (AUC) in the ROC analysis was found for C-peptide, followed by age and BMI (0.78, 0.68 and 0.66 respectively).

Conclusions: At diagnosis of diabetes, C-peptide was superior to age and BMI in discriminating between autoimmune and non-autoimmune diabetes. C-peptide increased significantly with BMI and age, latter also within each BMI group. Most of the adults had normal or high levels of C-peptide at presentation of diabetes among the autoimmune patients.

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Figures

Figure 1
Figure 1
(A) Mean fasting C-peptide (nmol/l), per age and BMI group in non-autoimmune diabetes. (B) Mean fasting C-peptide, including 95% confidence intervals, per antibody positivity; all in adults with newly diagnosed diabetes. **P<0.001.
Figure 2
Figure 2
Prevalence of antibodies per age group in percent (A) and absolute numbers (B) in adults with newly diagnosed diabetes.
Figure 3
Figure 3
ROC analysis of C-peptide, BMI and age to identify subjects that are autoimmune.
See this image and copyright information in PMC

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