B-244 Analytical Performance and Method Comparison Evaluation of a New High Throughput Fully Automated Plasma GFAP Immunoassay

Background Glial Fibrillary Acidic Protein (GFAP) levels are shown to be an indicator of neurologic injury in conditions like Traumatic Brain Injury (TBI) and stroke and as a marker of disease progression in neuromuscular disorders such as multiple sclerosis. Plasma GFAP is also implicated in detecting AD pathology, correlating to the clinical stage of the disease. The performance characteristics of the plasma GFAP immunoassay currently being developed on Beckman Coulter Access 2 and DxI 9000 analyzers are described. Methods 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 and washed, and then a chemiluminescent substrate is added. The light generated is directly proportional to the GFAP concentration in the sample. The assay time to the first result is ∼30 minutes. Analytical performance evaluation and method comparison across different platforms was performed. 43 EDTA plasma samples, consisting of 19 Alzheimer’s Disease (AD) patient samples and 24 age-matched healthy normal samples, were evaluated. Results The prototype GFAP assay has a targeted analytical measuring range of 1.0 pg/ml to approximately 700.0 pg/ml (up to 10,000 pg/ml). All normal samples were quantified with 90% measuring below 20.0 pg/ml and a low dose coefficient of variation <4.0%. A comparison of the prototype GFAP assay on DxI 9000 and Access 2 analyzers shows 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 Access 2 and DxI 9000 assays. The dose ratio of the median of AD over the median of normal samples for Access 2 and DxI 9000 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. Conclusions The prototype GFAP assay provides fast, highly sensitive, and precise results in an automated immunoassay on the Beckman Coulter Access 2 and DxI 9000 platforms. The prototype plasma GFAP assay holds promise for diagnosing and monitoring various neurodegenerative diseases, including AD.