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Objective: To evaluate an approach to measure β-cell function by frequent testing of C-peptide concentrations in dried blood spots (DBSs). Patients: Thirty-two children, aged 7 to 17 years, with a recent diagnosis of type 1 diabetes. Design: Mixed-meal tolerance test (MMTT) within 6 and again at 12 months after diagnosis, with paired venous and DBS C-peptide sampling at 0 and 90 minutes. Weekly DBS C-peptide before and after standardized breakfasts collected at home. Results: DBS and plasma C-peptide levels (n = 115) correlated strongly (r = 0·91; P < 0.001). The Bland-Altman plot indicated good agreement. The median number of home-collected DBS cards per participant was 24 over a median of 6.9 months. Repeated DBS C-peptide levels varied considerably within and between subjects. Adjustment for corresponding home glucose measurements reduced the variance, permitting accurate description of changes over time. The correlation of the C-peptide slope over time (assessed by repeated home DBS) vs area under the curve during the two MMTTs was r = 0.73 (P < 0.001). Mixed models showed that a 1-month increase in diabetes duration was associated with 17-pmol/L decline in fasting DBS C-peptide, whereas increases of 1 mmol/L in glucose, 1 year older age at diagnosis, and 100 pmol/L higher baseline plasma C-peptide were associated with 18, 17, and 61 pmol/L higher fasting DBS C-peptide levels, respectively. In addition, glucose responsiveness decreased with longer diabetes duration. Conclusion: Our approach permitted frequent assessment of C-peptide, making it feasible to monitor β-cell function at home. Evaluation of changes in the slope of C-peptide through this method may permit short-term evaluation of promising interventions.

Original publication

DOI

10.1210/jc.2018-00500

Type

Journal article

Journal

J Clin Endocrinol Metab

Publication Date

01/09/2018

Volume

103

Pages

3350 - 3358

Keywords

Adolescent, Area Under Curve, Blood Glucose, Blood Glucose Self-Monitoring, C-Peptide, Child, Correlation of Data, Diabetes Mellitus, Type 1, Dried Blood Spot Testing, Fasting, Feasibility Studies, Female, Humans, Male, Time Factors