HealthDay News — C-peptide responses to mixed-meal tolerance tests are reliable surrogates of insulin secretion, according to a study published online July 15 in Diabetes Care.

Wei Hao, MD, PhD, from the Benaroya Research Institute at Virginia Mason in Seattle, and colleagues sought to describe the natural history of residual insulin secretion in type 1 diabetes TrialNet participants over four years from diagnosis. Data were analyzed for 407 subjects.

The researchers found that over four years, the percentage of individuals with stimulated C-peptide of ≥0.2 nmol/L or detectable C-peptide of ≥0.017 nmol/L continued to decline; this was influenced by age. Only 5% maintained their baseline C-peptide secretion at four years. Over time and with age there was variation in the expected inverse relationships between C-peptide and glycated hemoglobin (HbA1c) or insulin doses. Age and time from diagnosis also influenced combined clinical variables, such as insulin dose-adjusted HbA1c (IDAA1C) and the relationship between IDAA1C and C-peptide. Models incorporating these clinical measures were not able to fully predict C-peptide responses.

“Current trials of disease-modifying therapy for type 1 diabetes should continue to use C-peptide as a primary end point of β-cell secretory function,” the authors write. “Longer duration of follow-up is likely to provide stronger evidence of the effect of disease-modifying therapy on preservation of β-cell function.”

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