Comparison of chromogranin-a levels determined by different test systems in patients with prostate diseases

Introduction. Chromogranin-A (CgA) is the most popular marker for neuroendocrine tumors. CgA demonstrates acceptable diagnostic value in neuroendocrine differentiation (NED) of prostate cancer (PC). At the same time there are conflicting data in the literature on NED detection frequency in PC patients, based on blood serum CgA level, which may be the result of variability of testing methods. There are two widely used blood serum CgA detection methods: DAKO (Denmark) and Euro-Diagnostica (Sweden). According to the producing companies’ data, CgA reference values are: for Euro-Diagnostica (ED) - 0-3 nmol/L, for DAKO - 2-18 U/L. During our previous studies we had a problem with interpreting CgA values defined by different testing methods, which resulted in diagnostic errors. That is why the main purpose of this work is to compare CgA values, defined by using DAKO and ED testing methods in various prostate diseases. Methods and Materials. The samples from 84 prostate disease patients and 29 healthy volunteers were analyzed. CgA level for all patients was defined using both DAKO and ED testing methods in the same blood sample. Results. Prevalence of the number of patients (10-40%) with elevated CgA level has been found with DAKO testing method, compared to ED testing method. Linear regression analysis revealed functional link and defined equations for DAKO and ED CgA values coordination. The ED method reference value of 3.0 nmol/L corresponds to the DAKO value of 28 U/L (not to the DAKO value of 18 U/L, indicated by the producing company). Applying coordinated reference DAKO CgA values we have managed to get CgA values close to those obtained with ED testing method. Conclusions. Officially claimed high CgA reference value for DAKO (18 U/L) is not exactly correct and leads to hyper-diagnostics in NED of prostate cancer. Mathematically corrected max CgA level according to DAKO test method data is 28 U/L.