Development and Application of Reference Measurement Procedures for C-peptide and Insulin in Human Serum

The final goal of the research presented in this dissertation is to solve the current problems existing in the clinical laboratory derived from the lack of comparability of results when different methodologies are used. These may be caused by the lack of standardization or the presence of specificity problems in the used in-vitro diagnostic systems. These differences in measurement results lead to the problem that clinicians can not make use of common reference intervals and treatment strategies. The solution to this problem is trueness based standardization via a Reference Measurement System. A key step of this Reference Measurement System is the split sample method comparison with a Reference Measurement Procedure. Because of the aforementioned, the major objectives of this dissertation were the development and application of Reference Measurement Procedures for C-peptide and insulin in human serum. The context in which these objectives are described is the so-called 'diabetes epidemic' that gradually affects humans worldwide and consequently increases the interest for routine C-peptide and insulin determinations. For peptides and proteins it is state of the art to use isotope dilution-liquid chromatography/tandem mass spectrometry as Reference Measurement Procedure. We were able to develop measurement procedures based in this technique for C-peptide and insulin that fulfilled the quality specifications required for their use in the standardization of commercial immunoassays used in the clinical laboratory