Evaluation of the Current State of Thyroid Hormone Testing in Human Serum—Results of the Free Thyroxine and Thyrotropin Interlaboratory Comparison Study
Authors' conclusion
The comparison among fT4 assays emphasizes the need for measurement standardization to improve accuracy and comparability.
Study context
- Population
- 41 blinded individual-donor sera (incl. one from a pregnant woman, free thyroxine (fT4) only) and three serum pools; fT4 11.3–32.1 pmol/L, TSH 0.337–21.6 mIU/L21 fT4 and 17 TSH assays
- Comparison
- FT4 immunoassays (IAs) and laboratory-developed tests (LDTs) vs CDC FT4 reference measurement procedure (RMP); TSH IAs vs TSH all-lab mean (ALM)
- TSH IAsn = 17
- Outcome
- Performance (median bias) of fT4 assays vs CDC fT4 RMP, pre-recalibration
Methodological detailsblinded individual-donor sera, Passing-Bablok regression, pre- and post-recalibration
- Blinded individual-donor sera
- Passing-Bablok regression
- Pre- and post-recalibration
Main finding
As reported in the abstract
Median bias of fT4 assays to RMP, pre-recalibration
fT4 IAs
−20.3%
median · CI −21.5%–-19.4%
LDTs
−4.5%
median · CI −6.1%–-3.2%
- Individual-donor sera classified uniformly by all fT4 assays (poor inter-assay agreement)
- 21 out of 40
Further findings
Median
| Outcome | fT4 IAs | fT4 LDTs | TSH IAs |
|---|---|---|---|
| Median bias of fT4 assays to RMP, post-recalibration | −0.2 (CI −1.2%–0.6%) | −0.3% (CI −2.5%–1.4%) | — not stated in the abstract |
| Median bias of TSH measurements to ALM, pre-recalibration | — not stated in the abstract | — not stated in the abstract | −1.2% (CI −1.8%–-0.4%) |
— not stated in the abstract
- Median bias of fT4 assays to RMP, post-recalibration — Individual-donor sera correctly classified by all tested IAs and LDTs post-recalibration
- 33 out of 40
Median bias of TSH measurements to ALM, pre-recalibration
- Good classification agreement among TSH assays
Original publication
Evaluation of the Current State of Thyroid Hormone Testing in Human Serum—Results of the Free Thyroxine and Thyrotropin Interlaboratory Comparison Study. Thyroid. Published 7 May 2025. doi:10.
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