[C-peptide measurement in the classification of diabetes mellitus and in the assessment of requirements for insulin treatment].

C-peptide and insulin are secreted in equimolar amounts from the beta-cells in the pancreas. Therefore, measurement of C-peptide in plasma can be used to estimate endogenous insulin secretion also in insulin treated diabetic subjects. From a clinical point of view, it is of especial interest to use measurements of C-peptide in the discrimination between diabetic subjects with and without insulin requirements. Such measurements are, however, difficult to interpret. Thus, plasma C-peptide values depend apart from C-peptide secretion also on C-peptide clearence, technical procedures, and during unsteady state conditions also on the C-peptide volume of distribution. In clinical practice, it is recommended only to measure basal plasma C-peptide and these values should be interpreted with caution. Generally, values below 0.2 nmol/l suggest insulin requirement while values above 0.5 nmol/l suggest non-insulin requirement. Patients with intermediate basal plasma C-peptide values should be evaluated more closely for example in hospital. Measurement of C-peptide should, however, be restricted to certain selected patients in whom the clinical classification is uncertain.