Glucose and C-peptide Changes in the Peri-Onset Period of Type 1 Diabetes in the Diabetes Prevention Trial-Type 1

Abstract

Objective: We examined metabolic changes in the period immediately following the diagnosis of type 1 diabetes (TID) and in the period leading up to its diagnosis in Diabetes Prevention Trial-1 (DPT-1) participants.

Research Design and Methods: The study included oral insulin trial participants and parenteral insulin trial controls (n=63) diagnosed with a 2-hr diabetic oral glucose tolerance test (OGTT) that was confirmed by another diabetic OGTT within three months. Differences in glucose and C-peptide levels between the OGTTs were assessed.

Results: Glucose levels increased at 90 (p=0.006) and 120 minutes (p<0.001) from the initial diabetic OGTT to the confirmatory diabetic OGTT (mean±SD interval: 5.5±2.8 weeks). Peak C-peptide levels fell substantially between the OGTTs (median change: -14.3%, p<0.001). Among the 55 individuals whose last non-diabetic OGTT was approximately six months prior to the initial diabetic OGTT, peak C-peptide levels decreased between these two OGTTs (median change: -14.0%, p=0.052). Among those same individuals the median change in peak C-peptide levels from the last normal OGTT to the confirmatory OGTT (interval: 7.5±1.3 months) was -23.8% (p<0.001). Median rates of change in peak C-peptide levels were 0.00 ng/ml/month (p=0.468, n=36) from approximately 12 months to 6 months before diagnosis, -0.10 ng/ml/month (p=0.059, n=55) from 6 months before diagnosis to diagnosis, and -0.43 ng/ml/month (p=0.002, n=63) from the initial diabetic OGTT to the confirmatory diabetic OGTT.

Conclusion: It appears that post-challenge C-peptide levels begin to decrease appreciably in the six months prior to diagnosis and decrease even more rapidly within three months after diagnosis.