C-peptide levels and the prevalence of islets autoantibodies in children with type 1 diabetes mellitus with different duration of the disease

Abstract

BACKGROUND : Type 1 diabetes mellitus (T1DM) is characterized by the development of absolute insulin deficiency. In some patients residual insulin secretion may persist for a long time. C-peptide is a widely used to measure the pancreatic beta cells function, in clinical practice and in research studies. AIM : To assess C-peptide levels and presence of islets autoantibodies (Ab) in children with different duration of T1DM and to identify factors associated with the preserved secretion. MATERIALS AND METHODS : Single-center cross-sectional study including data from 703 cases of children with T1DM, examined in the Endocrinology Research Center in 2016-2020, who was underwent a study of C-peptide levels and was positive for one or more islets antibodies (ZnT8, IA-2, GAD, ICA, IAA). There were 3 groups of patients: 1st — T1DM duration < 1 year, 2nd — from 1 to 5 years, 3rd — > 5 years. RESULTS : The median of the fasting C-peptide level in the 1st group was 0.6 ng/ml [0.27; 1.09]; in the 2nd group — 0.2 ng/ml [0.01; 0.8]; in the 3rd group — 0.01 ng/ml [0.01; 0.037]. The preserved secretion of C-peptide (> 0.6 ng/ml) was determined in 51.4% in the 1st group, in 31.4% — in the 2nd group and in 11.4% in the 3rd group. In patients with obesity during the first year from the T1DM diagnosis C-peptide levels above 1.1 ng/ml was determined significantly more often (65.2%), as well as at the period of 1 to 5 years of the disease (35.7%), compared with children with normal BMI (18.5% and 14.5%, respectively) or overweight (15.7% and 19%, respectively), p <0.01. A negative correlation was found between C-peptide levels and the duration of T1DM (r = -0.489, p = 0.000), the daily dose of insulin (r = -0.637, p = 0.000), a positive association was found with the age of diagnosis of T1DM (r = 0.547, p = 0.000). The frequency of the presence of one type of islets autoantibodies in all groups was 29.5%, 2 types — 33.6%, 3 and more types — 36.9%. The titer of IA-2, ZnT8 decreased with the disease duration (p <0.05 and p <0.01, respectively), while the titer of ICA increased (p <0.01). No associations between the types, number, antibodies titer and C-peptide levels, age of disease manifestation were found. CONCLUSION : C-peptide levels in children with T1DM in groups with older age at diagnosis and with obesity is significantly higher for the first 5 years of the disease. The study have shown the titer of IA-2, ZnT8 is decreasing with the disease duration, in turn, the frequency of detection of ICA increases. No association between C-peptide levels and the type, number and titer of antibodies were found.