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J Clin Endocrinol Metab. 2018 Sep 1;103(9):3350-3358. doi: 10.1210/jc.2018-00500.

Frequent Monitoring of C-Peptide Levels in Newly Diagnosed Type 1 Subjects Using Dried Blood Spots Collected at Home.

Author information

1
University of Cambridge, Department of Paediatrics, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Cambridge, United Kingdom.
2
Department of Paediatric Diabetes and Endocrinology, Royal London Hospital, Barts Health NHS Trust, London, United Kingdom.
3
NIHR Cambridge Biomedical Research Centre, Core Biochemistry Assay Laboratory, Cambridge University Hospitals NHS Foundation Trust, Cambridge Biomedical Campus, Cambridge, United Kingdom.
4
Paediatrics, Northampton General Hospital NHS Trust, Northampton, United Kingdom.
5
Department of Paediatric Endocrinology and Diabetes, Birmingham Children's Hospital NHS Foundation Trust, Steelhouse Lane, Birmingham, United Kingdom.
6
Institutes of Metabolism and Systems Research, Vincent Drive, University of Birmingham, Birmingham, United Kingdom.
7
Centre for Endocrinology, Diabetes and Metabolism, Vincent Drive, Birmingham Health Partners, Birmingham, United Kingdom.
8
Paediatric Endocrinology, Oxford Radcliffe Hospitals NHS Trust, Headington, Oxford, United Kingdom.
9
JDRF/Wellcome Trust Diabetes and Inflammation Laboratory, Wellcome Trust Centre for Human Genetics, Nuffield Department of Medicine, NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, United Kingdom.
10
University of Cambridge MRC Biostatistics Unit Hub for Trials Methodology Research, Cambridge, United Kingdom.
11
Wellcome Trust MRC Institute of Metabolic Science, Cambridge, United Kingdom.

Abstract

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.

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