[Clinical value of C-peptide determination]

The classification of newly diagnosed diabetic patients as type I (insulin-dependent) or type II (non-insulin-dependent) diabetes and the implied therapeutical consequences there of are based on clinical observations and laboratory tests. In case differential diagnosis is difficult, the measurement of the c-peptide secretion to assess beta-cell capacity can be helpful. For adequate control especially after long-standing diabetes in obese patients it is important to identify patients with potential secondary drug failure. Poor compliance with diet is thought to be a major reason for poor response to treatment. On the other hand, diabetics with poor control because of deterioration of beta-cell function must be distinguished. In these situations the measurement of c-peptide concentrations may contribute to identify the need for insulin treatment. As a result the development of diabetic complications can be retarded and beta-cell function can be preserved by adequate insulin therapy, whereas the consequences of hyperinsulinaemia in insulin treated patients not needing insulin can be avoided. In our opinion the c-peptide/glucose-quotient serves as simple, cost-effective and non-invasive method in the assessment of beta-cell capacity. Insulin therapy is indispensable in the case of inadequate insulin secretion.