Objective:

To identify factors associated with C-peptide levels at the diagnosis of type 1 diabetes mellitus (T1DM).

Material and Methods:

Retrospective review of the clinical records of patients with newly diagnosed T1DM admitted to a Portuguese reference center between August 2010 and July 2019.

Results:

The study included 109 subjects, with a mean age at T1DM diagnosis of 8.6 years and 29.4% already showing puberty development. The mean body mass index (BMI) z-score was 0.09. Subjects presented a median fasting C-peptide level of 0.46 ng/mL and a median hemoglobin A1C (HbA1C) of 10.85%. Diabetic ketoacidosis was identified in 22% of patients. A positive correlation was found between fasting C-peptide levels and age at diagnosis (p<0.001) and between fasting C-peptide levels and BMI z-score (p=0.041). Higher C-peptide levels were found in overweight/obese (p=0.008) and pubertal (p<0.001) individuals. C-peptide levels were found to be correlated with serum bicarbonate (p=0.005) but not with venous pH, HbA1C, or previous symptom duration. No statistically significant differences were observed in fasting C-peptide levels according to gender, diabetes autoantibodies, T1DM family history, or seasonality.

Conclusion:

Older, pubertal, and overweight/obese children presented higher C-peptide levels. In the acute setting, serum bicarbonate was the biochemical parameter that best correlated with residual β-cell function.

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