B-153 Analytical Performance Evaluation of the Glial Fibrillary Acidic Protein immunoassays

Abstract

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein predominantly expressed in astrocytes and certain neural stem/progenitor cells within the central nervous system. Growing evidence indicates that serum/plasma GFAP is associated with traumatic brain injury, neurodegenerative diseases (e.g., Alzheimer’s disease and related dementias), ischemic stroke, and intracranial hemorrhage. Thus, accurate and convenient detection methods is crucial for clinical diagnostics. This study aims to evaluate the analytical performance of a quantitative GFAP immunoassay manufactured by Maccura Biotech Co., Ltd. (Chengdu, China). The GFAP immunoassay processed on the Maccura chemiluminescence analyzers was evaluated according to CLSI guidelines. Analytical sensitivity, including the limit of blank (LoB), limit of detection (LoD), and limit of quantitation (LoQ), was evaluated in accordance with CLSI EP17-A2 using blank and low-concentration samples. LoQ was defined as the lowest concentration meeting predefined imprecision criteria (CV less than 20%). Precision studies (repeatability and within-laboratory) were evaluated across human serum and quality control samples per CLSI EP05-A3; all samples were measured in duplicate, with two runs per day over 20 consecutive days. A reference interval study was performed based on guidance from CLSI C28-A3c28 with a general population from healthy individuals (over 18 years old). Method comparison with an established assay (Simoa) was performed according to CLSI EP09-A3, Passing-Bablok regression was applied to clinical samples covering a broad concentration range. Clinical performance was evaluated by testing the samples of disease against healthy individuals, a total of 75 participants were divided into two groups: 47 in the healthy group and 28 in the Alzheimer’s disease (AD) group. The LoB, LoD and LoQ were less than 5.0 pg/mL, 10.0 pg/mL and 15.0 pg/mL, respectively. Repeatability and within-laboratory precision coefficients of variation were 2.25% and 2.84% for QC 1 (99.8 pg/mL); 1.50% and 1.83% for QC 2 (2171.7 pg/mL); 2.23% and 2.70% for Human Sample 1 (86.9 pg/mL); and 1.63% and 2.26% for Human Sample 2 (1097.5 pg/mL). The reference interval study included a total of 300 individuals. The results indicated that reference values were age-dependent. For individuals under 60 years of age, the reference value (95th percentile) was 55.1 pg/mL (95% CI: 52.3 – 56.7 pg/mL, n=150), for those aged 60 years or older, it was 81.7 pg/mL (95% CI: 79.8 – 82.7 pg/mL, n=150). A total of 40 samples were analyzed using the Maccura GFAP assay and the Simoa GFAP assay. The Passing-Bablok regression equation was y = 17.685 + 0.697x, and the Pearson correlation coefficient was 0.994. The GFAP concentrations in the HC and AD groups were 34.71±15.14 pg/mL and 88.78±48.09 pg/mL, p<0.0001. The Maccura GFAP immunoassay exhibits high analytical sensitivity and robust precision across the clinically relevant measurement range. In addition, it demonstrates strong correlation with the Simoa assay. Importantly, clinical performance evaluation confirms its ability to accurately discriminate Alzheimer’s disease from the healthy controls.