Analytical goals for quantities used to assess thyrometabolic status

Area of Science:

• Clinical Chemistry
• Endocrinology
• Laboratory Medicine

Background:

• Intra-individual biological variation is key for setting analytical performance goals.
• Existing data on biological variation informs targets for total T4, free T4, total T3, free T3, and TSH.
• For analytes lacking biological variation data, goals can be derived from reference intervals or interlaboratory quality assessment schemes.

Purpose of the Study:

• To define analytical goals for imprecision and inaccuracy in thyroid hormone assays.
• To establish specific performance targets for key thyroid function tests.
• To guide the improvement of laboratory testing for thyroid disorders.

Main Methods:

• Derived analytical goals for imprecision as coefficients of variation (CV) based on intra-individual variation.
• Established stringent CV goals for total T4 monitoring during thyroxine replacement therapy.
• Utilized reference intervals and interlaboratory quality assessment data for analytes lacking biological variation data.

Main Results:

• Recommended CV goals for total T4, free T4, total T3, free T3, and TSH are ≤2.5%, ≤4.7%, ≤5.2%, ≤3.9%, and ≤8.1%, respectively.
• A more stringent CV goal of ≤1.4% is proposed for total T4 in thyroxine replacement therapy monitoring.
• CV goals for reverse T3 and thyroxine-binding globulin were set at ≤10.7% and ≤7.2%, respectively, based on reference values.

Conclusions:

• Achieving defined analytical goals is essential for reliable thyroid hormone measurements.
• Improved analytical performance enhances between-laboratory comparability and supports universal reference values.
• Assay detection limit reporting should be replaced with information on the working range meeting imprecision goals.