Biological variation of thyroid stimulating hormone, free triiodothyronine and free thyroxine in healthy subjects in Turkey

• Published in: Biochemia Medica 2025-02, Vol.35 (1), p.010706-104
• Main Authors: Yıldız, Raziye, Özkanay, Hayat, Arslan, Fatma Demet, Köseoğlu, Mehmet
• Format: Article
• Language: English
• Subjects: Adult; biological variation; Female; healthy people; Healthy Volunteers; Humans; Male; Middle Aged; Original; Reference Values; Thyroid Function Tests; thyroid hormones; Thyrotropin - blood; Thyroxine - blood; Triiodothyronine - blood; Turkey; Young Adult
• ISSN: 1330-0962; 1846-7482; 1846-7482
• DOI: 10.11613/BM.2025.010706

Biological variation (BV) data are necessary for interpretation of test results and assessment of analytical performance. We aimed to determine the BV estimates for thyroid stimulating hormone (TSH), free triiodothyronine (fT3) and free thyroxine(fT4) in healthy subjects in Turkey and compare them with the literature findings. A total of 21 Turkish healthy volunteers (12 males and 9 females) were included in the study. Blood samples were collected once a week for five weeks, and the analysis was performed using the chemiluminescent immunoassay method on an Advia Centaur XP (Siemens Diagnostic, Tarrytown, USA). Analytical variation (CV ), within-subject BV (CV ) and between-subject BV (CV ) were calculated. Analytical goals, individuality index (II) and reference change value (RCV) were derived from these data. Statistical analysis was performed using BioVar: BV analysis tool v.1.0. For TSH, fT3 and fT4, CV (confidence interval, CI) were 3.3% (2.9 to 3.8), 1.7% (1.5 to 1.9) and 2.7% (2.4 to 3.1); CV (CI) were 22.3% (19.3 to 26.3), 4.4% (3.8 to 5.3) and 5.1% (4.3 to 6.1); CV (CI) were 26.6% (19.2 to 39.8), 9.2% (6.9 to 13.6) and 8.2% (6.1 to 12.1), respectively. For TSH, fT3 and fT4, desirable total errors were 27.1%, 6.2% and 6.6%; II values were calculated as 0.84, 0.48 and 0.61; and RCV% values (decrease; increase) were - 40.3;67.6, - 10.4;11.6 and - 12.7;14.5, respectively. Our study provides updated BV data for thyroid function tests (TFTs) in healthy subjects in Turkey. As TFTs have shown a high degree of individuality, RCV should be preferred rather than population-based reference ranges in the assessment of serum concentrations. Our BV estimates were compatible with European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) BV meta-analysis data obtained using different immunoassay methods in different populations.