Harmonization of free thyroid hormone tests: a mission impossible?

Area of Science:

• Clinical Chemistry
• Endocrinology
• Laboratory Medicine

Background:

• Accurate in vitro thyroid function tests are essential for reflecting in vivo hormone activity (TSH, T3, T4).
• Assay results for thyroid hormones should be interpretable against consistent reference intervals, regardless of the measurement method.
• The IFCC Working Group for Standardization of Thyroid Function Tests aims to improve method performance and quality specifications.

Purpose of the Study:

• To discuss the IFCC Working Group's contribution to standardizing free triiodothyronine (FT3) and free thyroxine (FT4) assays.
• To evaluate the effectiveness of newly established reference procedures and materials in harmonizing thyroid function test results.

Main Methods:

• Establishment of a candidate reference procedure and commutable reference materials using donor sera.
• Measurement of reference materials using a gold standard method, multiple immunoassays, and equilibrium dialysis procedures.
• Recalibration of test results to eliminate assay-specific biases.

Main Results:

• Recalibration successfully reduced assay-specific biases relative to reference method values on average.
• Sample-related effects persisted among the different immunoassay methods tested.
• The findings represent an initial step towards harmonizing patient test results for FT3 and FT4.

Conclusions:

• The study provides a foundation for standardizing FT3 and FT4 assays through reference procedures and materials.
• Despite progress in bias reduction, further research is required to achieve complete harmonization of FT3 and FT4 testing.
• The ultimate goal of achieving reliable and consistent thyroid function test results remains under investigation.