Objective: To determine the extent of beta-cell function in youth with diabetes and GAD65 and/or IA2 autoantibodies.
Research design and methods: Fasting C-peptide levels from 2,789 GAD65- and/or IA2 autoantibody-positive youth aged 1-23 years from the SEARCH for Diabetes in Youth study were used. Preserved beta-cell function was defined on the basis of cut points derived from the Diabetes Control and Complications Trial (DCCT) (fasting C-peptide > or =0.23 ng/ml) and from the U.S. adolescent population of the National Health and Nutrition Examination Survey (NHANES) 5th percentile for fasting C-peptide (> or =1.0 ng/ml). We compared the clinical characteristics between those with and without preserved beta-cell function.
Results: Within the first year of diagnosis, 82.9% of youth had a fasting C-peptide > or =0.23 ng/ml and 31.2% had values > or =1.0 ng/ml. Among those with > or =5 years of diabetes duration, 10.7% had preserved beta-cell function based on the DCCT cutoff and 1.0% were above the 5th percentile of the NHANES population.
Conclusions: Within the 1st year of diagnosis, four of five youth with autoantibody-positive diabetes have clinically significant amounts of residual beta-cell function and about one-third have fasting C-peptide levels above the 5th percentile of a healthy adolescent population. Even 5 years after diagnosis, 1 of 10 has fasting C-peptide above a clinically significant threshold. These findings have implications for clinical classification of youth with diabetes as well as clinical trials aimed to preserve beta-cell function after diabetes onset.