Establishment and verification of reference intervals for Alzheimer's disease plasma biomarkers based on evaluation of pre-analytical procedures: a multicenter study.

INTRODUCTION: To establish and verify reference intervals (RIs) for Alzheimer's disease (AD) plasma biomarkers amyloid beta (Aβ) 40, Aβ42, phosphorylated tau 181 (p-tau181), p-tau217, and total tau (t-tau) after defining optimal pre-analytical procedures. METHODS: Pre-analytical procedures were assessed, including storage of whole blood and plasma under different conditions and freeze-thaw times. RIs were established using 738 samples, with grouping by sex and age (≤ 44, 45 to 59, ≥60 years), and verified with 120 samples from four clinical centers. RESULTS: Samples stored at 2°C to 8°C for 22 to 28 h or -20°C to -80°C for 30 days were stable. Though sex/age differences in biomarker levels existed, they did not require partitioning. RIs of Aβ40, Aβ42, p-tau181, p-tau217, and t-tau were 12.71 to 283.6, 2.313 to 25.96, 0.8342 to 18.36, 0.3351 to 4.310, and 0.8096 to 18.65 pg/mL, respectively. The verification rates of RIs with the multicenter cohort (n = 120) were 93.33% to 99.14%. DISCUSSION: The established RIs for Chinese adults can potentially facilitate the early diagnosis of AD. Highlights: Optimized pre-analytical procedures: Plasma levels of Aβ40, Aβ42, p-tau181, p-tau217, and t-tau are unstable at room temperature (25 ± 3°C) but remain stable for 22 to 28 h at 2°C to 8°C (fluctuation ≤10%). For long-term storage, -20°C to -80°C is suitable, with stability maintained for 30 days; ≤5 freeze-thaw cycles have minimal impact on biomarker levels.Established reference intervals (RIs) for healthy Chinese adults: Using non-parametric 2.5th to 97.5th percentiles, RIs were determined as follows: Aβ40 (12.71 to 283.6 pg/mL), Aβ42 (2.313 to 25.96 pg/mL), p-tau181 (0.8342 to 18.36 pg/mL), p-tau217 (0.3351 to 4.310 pg/mL), and t-tau (0.8096 to 18.65 pg/mL).Validated multicenter applicability: Verification with 120 samples from four clinical centers showed that 93.33% to 99.14% of samples fell within the established RIs, confirming broad applicability.No need for stratification by sex or age: Despite significant differences in some biomarkers between sexes (e.g., higher p-tau181/217 in males) and age groups (e.g., age-related increase in Aβ40), Harris-Boyd tests indicated no requirement for stratification, supporting combined RIs.Clinical value: These RIs and pre-analytical guidelines facilitate standardized early diagnosis, risk assessment, and therapeutic monitoring of AD in the Chinese population.