Second‐generation fully automated Elecsys cerebrospinal fluid immunoassays demonstrate high precision, reproducibility, and sample stability suitable for clinical use to aid Alzheimer’s disease diagnosis

Abstract

AbstractBackgroundBeta‐amyloid(1–42) (Abeta42) and phosphorylated tau 181 (pTau) cerebrospinal fluid (CSF) biomarker analysis is recommended alongside cognitive evaluation to aid Alzheimer’s disease (AD) diagnosis. For clinical use, CSF biomarker assays should demonstrate high precision/reproducibility and sample stability. This study evaluated precision, reproducibility, and sample stability of second‐generation fully automated Elecsys® CSF immunoassays.MethodFrozen/pooled CSF and PreciControl samples were analyzed using Elecsys β‐Amyloid(1–42) CSF II/Phospho‐Tau (181P) CSF immunoassays on cobas e 601 (Roche Diagnostics International Ltd). pTau/Abeta42 ratios were calculated. Precision was evaluated at one site per Clinical and Laboratory Standards Institute (CLSI) EP02‐A3 (two runs/day in duplicate over 21 days; n=84). Reproducibility was determined per CLSI EP05‐A3 over five days using a single lot across three sites (site‐to‐site)/three lots at one site (lot‐to‐lot). Coefficients of variation (CVs)/standard deviations (SDs) for repeatability/intermediate precision/reproducibility were calculated using variance component analysis. Sample stability was determined from fresh CSF, collected per manufacturer's instructions. Baseline measurements were taken <6 hours after lumbar puncture and follow‐up measurements (from stored aliquots) at defined intervals for ≤8 days at room temperature (RT; 25°C; n=13), ≤15 days at 6°C (n=14), and ≤13 weeks at ‐20°C (n=25). Storage stability was determined from percent recoveries/ordinary linear regression.ResultRepeatability CVs were <2.4% and <1.9% for Abeta42 and pTau immunoassays, respectively, and <2.4% for pTau/Abeta42 ratio. Intermediate precision CVs were <3.3% and <3.7% for Abeta42 and pTau immunoassays, respectively, and <3.9% for pTau/Abeta42 ratio. Site‐to‐site reproducibility CVs were <5.1% and <3.6% for Abeta42 and pTau immunoassays, respectively, and <6.5% for pTau/Abeta42 ratio (Table 1). For the Abeta42 immunoassay, lot‐to‐lot reproducibility CVs were <5.4%, except for one sample pool (mean concentration: 322 pg/mL; SD: 34.1 pg/mL; Table 2). Lot‐to‐lot reproducibility CVs were <3.6% for the pTau immunoassay and <6.0% for pTau/Abeta42 ratio. At maximum sample storage duration (8 days at RT/15 days at 2−8°C), median recoveries of 95%/98% were observed for Abeta42 and 97%/99% for pTau immunoassays. Stability assessment at ‐20°C is ongoing.ConclusionThe Elecsys immunoassays demonstrated high precision/reproducibility, supporting clinical use in AD diagnosis. Conservative recommendations for sample storage are 5 days at RT/14 days at 2−8°C.