Comparison of thyroid hormones reference intervals based on thyroid antibody levels: A multicenter study

This study aimed to determine reference intervals (RI) for thyroid hormones based on thyroid antibody levels using different autoanalyzer kits.

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.

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.

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.