Evaluation of a new fully automated one-step C-peptide chemiluminescence assay (LIAISON C-Peptid)

The determination of C-peptide, a 31 amino acid fragment of proinsulin which is a byproduct of insulin formation, is used as a marker for insulin secretion. Clinically, the determinations are performed to detect autonomous insulinoma, factitious hypoglycemia, and in general to assess the function of beta-cells in patients with diabetes mellitus. The analysis is frequently performed by radioimmunoassays (RIA), which have several disadvantages, for instance the use of radioactivity and time and resource requirements. We performed an evaluation of a new fully automated chemiluminescence assay (LIAISON C-Peptid, Byk-Sangtec) at two clinical sites, in Germany and Italy, with regard to imprecision and clinical relevance of the obtained data, and the correlation with a standard RIA method and another chemiluminescence test. The new assay showed a good correlation with the RIA (r = 0.950) and the chemiluminescence assay (r = 0.967). The intra-assay variability and inter-assay variability was 3.5% and 8.7% in Germany, and 2.4% and 9.6% in Italy. The clinical evaluation of samples derived from 19 oral glucose tolerance tests, 13 insulin suppression tests, and 2 insulin secretion stimulation tests revealed a clinical specificity of 100%, i.e. all cases resulted in the same clinical diagnosis with all tests. With regard to the practical performance of the assays, the new chemiluminescence test, as a single-step fully automated method, offered the advantage of being a non-radioactive, less complex and much faster method than the RIA and also had timely advantages over the comparative chemiluminescence test. In general, the new LIAISON chemiluminescence assay compared favorably with the RIA and comparative chemiluminescence test and offers an attractive alternative for C-peptide analysis.