The differences in chromogranin A (CgA) concentrations measured in serum and in plasma by IRMA and ELISA methods

Chromogranin A (CgA) is regarded as a major, nonspecific marker of neuroendocrine tumors (NET). Its estimation appears helpful for diagnostic purposes and is particularly useful for monitoring the treatment of NET. It must be kept in mind, however, that various factors, drugs, or coexisting diseases may influence the outcome of CgA measurement in blood. One such analytical factor is the sort of studied biological material, whether it is plasma or serum. The aim of our study was to compare directly the results of CgA concentrations measured in serum and in plasma by IRMA and ELISA.

We analysed 122 samples of EDTA-plasma and 122 samples of serum by IRMA method, 20 samples of EDTAplasma and 20 samples of serum by IRMA and ELISA, 25 heparinised-plasma samples and 25 samples of EDTA-plasma by IRMA and ELISA methods, and 8 EDTA-plasma, heparinised-plasma, and serum samples by IRMA and ELISA. The material for comparative study was obtained during the same blood collection from the same subjects (volunteers and patients with NET). CgA was measured with the use of kits manufactured by CIS bio International (France).

CgA concentrations were markedly higher in plasma than in serum. Using the IRMA method, the difference in the CgA range between 10-100 ng/mL approached 20-70% (median 61 v. 42), in the range 101-300 ng/mL--12-60% (median 147 v. 101), and in the CgA range 301-1076 ng/mL--14-40% (median 486 v. 356). The differences between results in serum and plasma using ELISA were similar but slightly smaller. There was no significant difference between CgA levels in EDTA and heparinised-plasma samples, and the results of measurements performed by IRMA and ELISA in most cases were similar.

Referring each individual CgA result to the proposed reference range (or cut-off value) we must take into account whether the measurement is performed in plasma or in serum.