The establishment of specific reference intervals for serum transthyretin tetramer, misfolded proteins, and protein misfolding rate and its application in evaluating transthyretin amyloidosis patients.

Background: To accurately assess disease risk, specific reference intervals for transthyretin (TTR) tetramers, misfolded proteins, and protein misfolding rates are essential. This study aimed to establish reference intervals using a robust and traceable ultrahigh performance liquid chromatography (UPLC) method and to evaluate the distribution of these biomarkers in patients with transthyretin amyloidosis (ATTR).

Methods: Serum samples from 331 healthy Chinese individuals were included. Participants were stratified into two age groups: <60 years and ≥ 60 years. The reference intervals were determined following the Clinical and Laboratory Standards Institute (CLSI) EP28-A3.

Results: The established reference intervals for TTR tetramers, misfolded proteins, and protein misfolding rates revealed significant age- and sex-specific variations. In the < 60 years age group, the TTR tetramer reference intervals were 3.01-6.30 μmol/L for males and 2.62-5.39 μmol/L for females. Corresponding reference intervals for misfolded proteins were 0.24-1.43 μmol/L for males and 0.33-1.39 μmol/L for females, with protein misfolding rate upper limits of 26.32 % and 27.47 %, respectively. In the ≥ 60 years age group, TTR tetramer reference intervals from 2.56-5.48 μmol/L for males and 2.36-5.10 μmol/L for females. Misfolded protein reference intervals were 0.28-2.03 μmol/L for males and 0.29-1.59 μmol/L for females, while protein misfolding rate upper limits were 33.69 % for males and 30.64 % for females.

Conclusions: This study successfully established detailed, age- and sex-specific reference intervals for TTR tetramers, misfolded proteins, and protein misfolding rates, providing valuable references for clinical practice and further investigations into disease risk associated with TTR biomarkers.