Evaluation of a new immunoassay for chromogranin A measurement on the Kryptor system

BACKGROUND Chromogranin A (CgA) is a biomarker for neuroendocrine tumors (NETs). The aims of this study were to evaluate differences in measurement between the ThermoFisher Brahms CgA Kryptor assay and the CisBio assay and to investigate the influence of patient covariates. Temperature stability of CgA using both assays was determined. DESIGN AND METHODS 406 patients were analyzed for serum CgA using both assays. We performed a comparison study to determine whether several patient covariates (gender, use of protein pump inhibitors, impaired kidney function, referral department and tumor location) influenced the results. For the stability study, pooled serum samples were aliquoted and stored at different storage temperatures (room temperature, 4 °C and -20 °C) until assayed. In addition, 15 individual samples were evaluated after storage at 4 °C using the Kryptor assay. RESULTS Differences in measured concentrations between the assays were statistically significant. Passing & Bablok fit showed ln Y(Kryptor)=1.05 ln X(CisBio) - 0.20 with a bias of 1.0% after logarithmic transformation. Patient covariates were not associated. Patients׳ sera showed variable stability for CgA in the Kryptor assay at room temperature and 4 °C, whereas the recovery in the CisBio assay was stable at both temperatures. CONCLUSION Differences in measured CgA concentration between the assays could not be explained by the investigated patient covariates. Serum should be stored at -20 °C prior to determination using the Kryptor assay.