Stability of pro-gastrin-releasing peptide in serum versus plasma

Although serum assays for pro-gastrin-releasing peptide (ProGRP) assays have been commercially available in Japan for several years, the stability of ProGRP in serum and plasma has not been well documented. We investigated the stability of ProGRP in serum and plasma with fresh and stored (frozen) specimens, as well as the cause of the observed instability in serum.

ProGRP concentrations in fresh serum were decreased by 6-28% after room temperature storage for 2 h and by 8-32% after 2-8 degrees C storage for 24 h. The average change in ProGRP concentrations in fresh plasma was within +/-10% of baseline for more than 4 h at room temperature and for more than 24 h at 2-8 degrees C. The incubation of a serine protease, thrombin (activated blood coagulation factor II), in a buffer solution containing ProGRP caused decreases in ProGRP concentrations. Following the addition of phenylmethylsulfonyl fluoride, a serine protease inhibitor, to serum, the serum stability for ProGRP was similar to that in plasma. ProGRP is significantly more stable in plasma than in serum. We speculate that thrombin in serum is one of the factors that inactivate ProGRP in serum by proteolysis of the ProGRP antigen.

The use of plasma samples for ProGRP may improve the clinical reliability of this marker by minimizing preanalytical changes in ProGRP concentrations.