In all forms of diabetes, especially so in Type 1 diabetes (T1D), beta cell function is crucial for the course. The interest for residual beta cell function has been meagre, but increased in recent years with interventions to preserve function. Areas covered: Importance and clinical use of C-peptide in Type 1 diabetes. Data for this review were identified by searches of PubMed, and references from relevant articles using the search terms: "type 1 diabetes", "C-peptide", "beta cell function", "HbA1c", quality of life", "complications". Abstracts and reports from meetings were not included. Expert commentary: C-peptide may help to get a correct diagnosis, and it is of practical clinical value to know degree of residual insulin secretion to diminish the risk of severe hypoglycaemia and ketoacidosis. Evidence shows that even a quite reduced beta cell function may play an important role for quality of life, for metabolic balance/control, possibility to avoid complications and even for long-term survival. Furthermore, the evidence is increasing for C-peptide being a hormone per se.
Keywords: C-peptide; beta cell function; beta cell preservation; complications; hypoglycaemia; immune interventions; keto-acidosis; type 1 diabetes.