Different biological matrices (serum and plasma) utilization in consolidation processes: evaluation of seven Access immunoassays.

Background: The compatibility of immunoassay tests in different sample matrices is extremely important during the assay validation process. In this study, we investigated the interchangeability of some Access (and therefore all the UniCel Family platforms) assays between serum and plasma.

Methods: We tested approximately 200 samples in parallel between serum and lithium heparin plasma for seven analytes: alpha-fetoprotein (AFP), carcino-embryonic antigen (CEA), total prostate specific antigen (tPSA), free prostate specific antigen (fPSA), digoxin, progesterone and unconjugated estriol (uE3). We used the Access2 Immunoassay System (Beckman Coulter), a fully automated random access system with a chemiluminescent signal. We performed statistical comparative analysis using two commercially available programs, Analyze-it from Microsoft Excel and MedCalc Software, and a dedicated statistical program.

Results: Firstly, we showed the results of the statistical tests performed on each population to verify their distribution. Analysis by several statistical tests (Passing and Bablok regression, Youden and Bland and Altman diagrams, the Mountain plot and multivariate analysis) showed that all the assays studied were valid in both serum and lithium heparin plasma matrices.

Conclusions: As all Access and UniCel Family instruments use the same reagent packs, these results are transferable to all Beckman Coulter immunochemistry platforms, without a commutability problem between serum and plasma and without a need for establishment of a plasma reference interval.