Development of Tau-441-Certified Reference Materials by Three Independent Isotope Dilution Mass Spectrometry Strategies

Tau protein, a microtubule-binding protein, is an important biomarker of Alzheimer's disease (AD). Sensitive and accurate detection of Tau is crucial for the diagnosis and treatment of AD. Even though both immunoassays and mass spectrometry have revealed their advantages in biofluid Tau measurement, significant variation exists among results from different assays due to variability in selectivity or calibrators, which underlines the importance of establishing a traceability chain for Tau measurements. The development of Tau-related certified reference material (CRM) and the establishment of traceability could help to standardize clinical result variation, which could further provide an opportunity for unifying clinical diagnosis interval and cutoff values. In this study, Tau-441 solution CRM (NIM-RM 2901) with the certified value and uncertainty of (74.1 ± 3.6) μg g^-1 was developed with high-purity Tau-441 as the raw material. After purity and structure confirmation, three independent isotope dilution mass spectrometry strategies based on amino acids, signature peptides, and sulfur were employed to certify the candidate Tau-441 solution CRM. The candidate Tau-441 CRM showed good homogeneity, and satisfying stability was also demonstrated for at least 7 days at -20 °C and 13 months at -70 °C. The Tau-441 solution CRM (NIM-RM 2901) is primarily intended to be used for value assignment to secondary calibrators or CRMs with clinical matrix, which will help the early diagnosis of AD in the clinic.