B-250 Analytical and Diagnostic Performance Evaluation of Plasma pTau217 in a Clinical Diagnostic Laboratory

Blood-based biomarkers are a readily accessible and cost-effective screening tool for Alzheimer’s disease (AD). Phosphorylated tau 217 (pTau217) is a specific biomarker for diagnosis and differentiating of AD. It is also a reliable biomarker for facilitating more timely access to disease-modifying therapies. Here, we report the analytical and clinical performance of plasma pTau 217 using high-sensitivity methodologies in a clinical diagnostic laboratory.

The analytical performance, including precision, specificity, detection limits, and linearity, as well as analyte stability, was assessed. Plasma pTau217 levels were measured using ALZpath pTau217 assay on the Quanterix HD-X Simoa® platform or LUMIPULSE plasma pTau217 on the Lumipulse G1200 platform. Clinical Validation conducted at Neurocode USA & BC Neuroimmunology involving 263 samples with amyloid PET data, 219 healthy aging samples and 150 Pathology confirmed samples.

The mean plasma pTau 217 concentrations in healthy aging samples were 0.22 ± 0.08 ng/L. ALZpath pTau217 assay has an analytical measurement range of 0.06 - 10 pg/mL, with a limit of blank (LoB) of 0.0035 ng/L, a limit of detection (LoD) of 0.0074 ng/L, and a limit of quantification (LoQ) of 0.0600 ng/L. Its linearity extends from 0.19 to 2.8 ng/L, with repeatability demonstrating intra-laboratory precision above LoQ ≤ 20% CV. Stability is maintained at 4⁰C for ≤ 1 week, at room temperature for ≤ 24 hrs, at -20⁰C for ≤ 4 weeks, and at -80⁰C for ≤ 4 weeks, with freeze/thaw cycles tolerated up to 5 times. Furthermore, no interference was detected at the maximum concentrations tested for bilirubin, hemoglobin, biotin, and heterophilic antibodies. ROC analysis yielded an AUC of 0.92 to 0.93, identifying a suitable clinical cutoff of < 0.4 ng/L.

The outstanding clinical and analytical performance of pTau217 supports its adoption as a robust screening tool in clinical practice, facilitating accurate and reliable diagnosis of AD by clinicians.