New high throughput fully automated plasma GFAP immunoassay

Abstract Background The analytical performance characteristics for the plasma Glial Fibrillary Acidic Protein (GFAP) immunoassay currently under development on Beckman Coulter, Inc. Access2™ and DxI9000™ analyzers is described. Blood GFAP levels may be indicative of the extent of neurologic injury in diseases such as TBI and stroke and maybe used as a marker of disease progression in other diseases such as multiple sclerosis. Plasma GFAP outperforms its CSF counterpart in detecting AD pathology and correlation to the clinical stage of the disease Method The prototype GFAP assay is a one‐step sandwich assay utilizing an anti‐GFAP mouse monoclonal (MAb) antibody/alkaline phosphatase conjugate and paramagnetic particles coated with a complementary anti‐GFAP mouse MAb. Sample and reactants are incubated, washed, then a chemiluminescent substrate is added. The light that is generated is directly proportional to the GFAP concentration in the sample. The assay time to first result is ∼30 minutes. 43 EDTA plasma samples, consisting of 19 Alzheimer’s Disease (AD) patient samples and 24 age‐matched healthy normal samples, were evaluated. A method comparison was performed between Access2™ and DxI9000™ platforms. Result The prototype GFAP assay has a targeted analytical measuring range of 1.0 pg/ml to approximately 700.0 pg/ml (capable of measuring analyte up to 10,000 pg/ml). 100% of normal samples were quantified (90% measuring below 20.0 pg/ml), with low dose variability (<4.0% coefficient of variation). A comparison of the prototype GFAP assay on DxI9000™ against Access2™ gave a Passing‐Bablok slope of 0.94 (R=0.992) and an intercept of 0.37 pg/ml. Concordance analysis shows excellent agreement between the Access2™ and DxI9000™ assays. The dose ratio of the median of AD over the median of normal samples for Access2™ and DxI9000™ is 2.31 and 2.41, respectively, with AD patient median dose values of 14.3 pg/ml and 14.6 pg/mL, respectively, and normal sample median dose values of 6.2 pg/ml and 6.0 pg/mL, respectively. Conclusion The prototype GFAP assay provides fast, highly sensitive and precise results in an automated immunoassay on the Beckman Coulter Access2™ and DxI9000™ platforms. The prototype plasma GFAP assay could be used to both diagnose and monitor various neurodegenerative diseases such as AD.