C-peptide in the classification of diabetes in children and adolescents

Ludvigsson J, Carlsson A, Forsander G, Ivarsson S, Kockum I, Lernmark Å, Lindblad B, Marcus C, Samuelsson U. C‐peptide in the classification of diabetes in children and adolescents. Aim: To report C‐peptide results in newly diagnosed patients and the relation to clinical diagnosis of diabetes. Methods: A nation‐wide cohort, the Better Diabetes Diagnosis study was used to determine serum C‐peptide at diagnosis in 2734 children and adolescents. Clinical data were collected at diagnosis and follow‐up. C‐peptide was determined in a validated and controlled time‐resolved fluoroimmunoassay. Results: The clinical classification of diabetes, before any information on human leukocyte antigen, islet autoantibodies, or C‐peptide was received, was type 1 diabetes (T1D) in 93%, type 2 diabetes (T2D) in 1.9%, maturity onset diabetes of the young (MODY) in 0.8%, secondary diabetes (0.6%), while 3.3% could not be classified. In a random, non‐fasting serum sample at diagnosis, 56% of the patients had a C‐peptide value >0.2 nmol/L. Children classified as T2D had the highest mean C‐peptide (1.83 + 1.23 nmol/L) followed by MODY (1.04 ± 0.71 nmol/L) and T1D (0.28 ± 0.25 nmol/L). Only 1/1037 children who had C‐peptide 1.0 nmol/L for the classification of either T2D or MODY was 0.46 [confidence interval 0.37–0.58]. Conclusions: More than half of children with newly diagnosed diabetes have clinically important residual beta‐cell function. As the clinical diagnosis is not always straightforward, a random C‐peptide taken at diagnosis may help to classify diabetes. There is an obvious use for C‐peptide determinations to evaluate beta‐cell function in children with diabetes.