Establishment and verification of reference intervals for Alzheimer's disease plasma biomarkers based on evaluation...

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.

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.

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%.

The established RIs for Chinese adults can potentially facilitate the early diagnosis of AD.

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.