Objectives: This study aimed to determine reference intervals (RI) for thyroid hormones based on thyroid antibody levels using different autoanalyzer kits.
Methods: RI for Thyroid-stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3) were determined according to thyroid antibody levels and independently of thyroid antibody levels using the R statistical program and RefineR algorithm.
Results: Significant differences in RIs were found between antibody-positive (Ab(+)) and antibody-negative (Ab(-)) individuals. TSH RI varied most notably in Abbott and Siemens analyzers. In females, Abbott showed higher TSH RIs in the Ab(+) group (0.41-7.44 mU/L) than in Ab(-) (0.24-3.50 mU/L). In males, Roche and Beckman exhibited the greatest differences (Roche Ab(+): 0.19-5.77; Ab(-): 0.44-3.63; Beckman Ab(+): 0.12-5.23; Ab(-): 0.39-3.96 mU/L). For fT4, Roche showed increased RIs in females with Ab(+) status (11.42-20.42 vs. 10.34-19.35 pmol/L). In males, Beckman and Siemens autoanalyzers also indicated notable differences.
Conclusion: Antibody status significantly affects thyroid hormone RI, particularly for TSH. These findings highlight the need for antibody-specific RI and further standardization in establishing reference intervals.
Copyright: © 2026 Beyter et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.