Background

Even long-term Type 1 diabetes (T1D) can be associated with low level insulin production. Residual C-peptide may reduce risk of vascular complications and hypoglycaemia.  

Material and methods

Plasma C-peptide levels were measured in a cross-sectional study of 249 healthy controls (CON) and 365 T1D patients (F/M=198/167), aged 10-80 y, (mean±SD) 30±16 y, with T1D duration of 16±12 y. Of the T1D patients 129 had microvascular complications (CX+). HbA1c was 8.4±1.6% and 5.1±0.4% in T1D and CON respectively (p=0.00001). C-peptide levels were measured by ultra-sensitive ELISA (Mercodia, Sweden), with a low detection limit of 1.25 pmol/L (0.0038 ng/mL). C-peptide levels below OD of the lowest calibrator were expressed as ¼ of the concentration of the assay’s lowest calibrator as per manufacturer’s instructions (Technical Note 34-0144). C-peptide in CON and T1D were 547.1±1.2 pmol/L and 3.6±1.2 pmol/L respectively; p=0.0001. Undetectable C-peptide level frequency did not differ between CX+ and CX- groups. For T1D subjects with detectable levels C-peptide levels were lower in those with vs. without complications: 2.7±0.9 pmol/L and 4.4±0.6 pmol/L respectively, p=0.04. Subjects were divided into cohorts by age of T1D diagnosis (≤10, 10 to ≤20 and >20 y) and T1D duration (≤10, 10 to ≤20 and >20 y). C-peptide levels are shown in the table. Young age diagnosis (≤10 y.o.) was associated with higher rates of undetectable C-peptide, p=0.0001 vs. combined age T1D diagnosis 10 to ≤20y.o. and >20y.o. For T1D diagnosed in early childhood C-peptide levels are higher in those with longer T1D duration, whilst for those diagnosed >20 y longer T1D duration is associated with lower C-peptide.

Conclusions

Although cross-sectional, our results are supportive of more complete beta cell loss in younger onset T1D, and potential beta cell regeneration. Residual C-peptide levels are higher in T1D subjects without vs with complications. Longitudinal studies are merited.