Reference limit of thyrotropin (TSH) and free thyroxine (FT4) in thyroperoxidase positive and negative subjects: A population based study

• Published in: Journal of endocrinological investigation 2013-12, Vol.36 (11), p.950-954
• Main Authors: Amouzegar, A., Delshad, H., Mehran, L., Tohidi, M., Khafaji, F., Azizi, F.
• Format: Article
• Language: English
• Subjects: Adult; Aged; Autoantibodies; Endocrinology; European Continental Ancestry Group; Female; Humans; Iodide Peroxidase - immunology; Iran; Male; Medicine; Medicine & Public Health; Metabolic Diseases; Middle Aged; Original Article; Prospective Studies; Reference Values; Thyroid Gland - immunology; Thyrotropin - blood; Thyroxine - blood
• ISSN: 0391-4097; 1720-8386
• DOI: 10.3275/9033

Background: Current reference values for thyroid function tests are based on data from different ethnicities and geographical areas. The aim of the present study was to determine reference intervals for thyrotropin (TSH) and free T 4 (FT 4 ), based on the criteria of the National Academy of Clinical Biochemistry (NACB) in an Iranian population. Material and methods: This study was conducted within the framework of Tehran Thyroid Study (TTS), an ongoing prospective cohort of 5704 randomly selected individuals, age ≥20 yr. A total of 2199 individuals (43.3% male, 56.7% female), based on NACB criteria were included in this study. Reference limit analysis was performed for the negative thyroid peroxidase antibody (TPOAb) group. Results: After applying all exclusion criteria except TPOAb positivity (10.5%), data of 2459 participants remained for analysis. Of these, 953 (43.3%) were males and 1246 (56.7%) were females; the mean±SD age was 43.53±14.16 yr. The mean±SD and median+IQR for TSH were 1.77 mU/l ±1.24 and 1.46 (0.93–2.23) mU/l, respectively. The 2.5 th and 97.5 th percentiles TSH were 0.32 mU/l and 5.06 mU/l respectively. The mean±SD and median (IQR) for FT 4 for all negative TPOAb subjects were 1.19±0.16 and 1.18 (1.08–1.31) ng/dl respectively. Conclusion: Reference ranges for thyroid function tests need to be derived from national databases. This study determined age and sex specific TSH and FT 4 reference ranges in a Tehranian population, which could eventually enable clinicians to classify patients more appropriately.