Neurology 2 plex b

Duplicate blood samples were analyzed in-house (Quanterix SRX analyzer), blinded to all clinical and demographic data, using single molecule array (Simoa) technology for p-tau181 (Quanterix Advantage v2 kit), GFAP, and NfL (Quanterix Neurology 2-Plex B). Our group previously reported separate plasma NfL data in a smaller sample of the 1FLADRC.^{19 (link)} NfL data are reported here in a larger cohort with different study aims and using a different Quanterix Simoa assay. Samples with coefficients of variation >20% were excluded (p-tau181: 10.8% of sample, GFAP: 7.4%, NfL: 6.3%). Additional sample collection and processing details are provided in Supplementary Methods.

We performed CSF biomarker assays using the Simoa SR-X platform^{1 (link),20 (link)} and plasma biomarker assays using the Simoa HD-X platform (both Quanterix). Samples were assayed in duplicate per the package insert instructions using the following Quanterix kits: Neurology 3-Plex A (catalog No. 101995) for Aβ42, Aβ40, and T-tau; pTau-181 V2 Advantage (catalog No. 103714) for P-tau181; and Neurology 2-Plex B (catalog No. 103520) for GFAP and NfL. Ratios of Aβ42/Aβ40, T-tau/Aβ42, and P-tau181/Aβ42 were calculated. Cerebrospinal fluid positivity for AD was determined using the CSF P-tau181/Aβ42 optimal cut point of 0.223 established in our laboratory. This CSF cut point is derived from receiver operating characteristic (ROC) analysis of a validation group of combined autopsy cases (n = 20) and amyloid PET cases (n = 59) with CSF biomarkers, including Aβ40, Aβ42, T-tau, P-tau181, and NfL (using Quanterix kit 103400), measured on the SR-X system. The area under the curve (AUC) was best for P-tau181/Aβ42, at 0.88 (0.79-0.97) with a Youden index of 0.82. At the P-tau181/Aβ42 cut point of 0.22, sensitivity was 0.95 and specificity was 0.87.