Comparison of chromogranin A (CgA) levels in serum and plasma (EDTA2K) and the respective reference ranges in healthy males.

INTRODUCTION Chromogranin A (CgA) is a major, nonspecific marker of neuroendocrine tumours (NET). There are a few routinely used assays for the measurement of CgA concentration in serum or plasma. These assays differ in analytical techniques (radioimmunoassay, ELISA, CLIA, TRACE), have different calibrators, and use different antibodies which recognise different epitopes of CgA molecule. Our study was designed to confirm the noted earlier differences in CgA levels measured in serum and plasma, and to establish respective reference ranges in a group of healthy males. MATERIAL AND METHODS In 145 male blood donors (age 19-61 years, mean = 35.7), blood was collected into two tubes: one with EDTA2K (plasma) and one with clot activator (serum). Chromogranin A was measured by immunoradiometric kit (CIS bio, France). RESULTS In blood donors, the median (and the range) of CgA concentration were as follows for serum samples - 42.0 ng/mL (16-108 ng/mL) and for plasma (EDTA2K) samples - 58.0 ng/mL (23-153 ng/mL). The differences between serum and plasma ranged 15-75% (median 26%). Plasma CgA levels were significantly higher in relation to serum CgA levels (p < 0.0001). Correlation of CgA in serum and plasma was r = 0.8493; p < 0.01. The reference ranges for CgA measured in serum and plasma in males, expressed as 2.5 to 97.5 percentiles, were: 21.0-108.0 ng/mL and 31.0-153.0 ng/mL respectively. CONCLUSIONS 1. Significant differences in the concentrations of CgA measured in plasma and in serum demand the application of separate reference ranges adjusted to the type of investigated material. 2. Each laboratory should recommend only one sort of sample material for CgA assay.