Absolute quantification of C-reactive protein in human plasma derived from patients with epithelial ovarian cancer utilizing protein cleavage isotope dilution mass spectrometry.

A method employing protein cleavage isotope dilution mass spectrometry (PC-IDMS) was developed for quantification of C-reactive protein (CRP) in human plasma. This method was completed without the use of immunoaffinity chromatography or size exclusion chromatography, as previous mass spectrometric methods for the quantification of CRP have employed. A total of 110 human plasma samples were analyzed with PC-IDMS via 1-D nanoLC-MS/MS using a 30 min gradient with a triple quadrupole mass spectrometer operated in selective reaction monitoring (SRM) mode. The results from this newly developed method were compared to results generated from an enzyme-linked immunosorbent assay (ELISA) performed by an independent CLIA certified laboratory. The comparison of these results generated an R(2) = 0.9708 which indicates successful quantification of CRP from human plasma utilizing the methodology described herein. Interestingly, the PC-IDMS method provided concentration values that were approximately 10x the concentration reported by the ELISA method, which demonstrated that the method of detection is an important consideration when determining reference ranges of a particular analyte. In addition, data is shown that illustrates that, as epithelial ovarian cancer (EOC) progresses from stage I to stage IV, mean levels of CRP increase.