An Italian program of external quality control for chromogranin A (CgA) assay: State of the art of CgA measurement

Abstract

Chromogranin A (CgA) is a secretory protein produced by many neuroendocrine cells. Circulating levels of CgA have been found to be elevated in a variety of neuroendocrine tumors and may facilitate the diagnosis and management of patients with functioning as well as non-functioning forms. However, up to now the analytical methods used for assaying intact CgA and CgA-derived peptides in the circulation of patients have not been monitored in Italy by an external quality control program. Within the framework of a Ministry of Health project an external quality control program was developed to investigate the state of the art of CgA determination in Italy and to monitor the performance of laboratories carrying out this assay. This paper deals primarily with the former of these aspects. Every laboratory received the study protocol together with a questionnaire to be returned before receipt of the samples to be assayed. Serum and plasma samples obtained from a pool of routine specimens were prepared at three different concentrations of CgA, aliquoted, frozen at -80 degrees C and mailed in dry ice to the participating laboratories. Of the 43 laboratories, 21 used IRMA, 21 used ELISA and one used RIA. There was a wide range in the time of kit utilization and the number of samples assayed per year, which indicated that the participating group was heterogeneous with regard to their experience in the determination of CgA. Most laboratories routinely used serum and plasma for IRMA and ELISA, respectively, and different data fitting approaches were employed. Further analyses will investigate the possible influence of these preanalytical factors on laboratory performance.