Thyroid hormone reference intervals and the prevalence of thyroid antibodies

Authors: AYDAN ÇELEBİLER, SİBEL BİLGİLİ, EMİNE ÖMÜR ERKIZAN, HURİYE SERİN, MUHAMMET BAYSAL KARACA

Abstract: To establish new reference intervals for thyrotropin (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) on the Beckman Coulter DxI 800 in healthy Turkish adults and assess the prevalence of laboratory evidence of thyroid antibodies in this population. Materials and methods: Specimens were obtained from 619 healthy volunteers (338 females, 281 males).The study was conducted with health care professionals and their relatives, The mean age of all the subjects was 34.7 and the median was 31 years, with ages ranging from 15 to 84. Moreover, the subjects had no evidence of thyroid autoimmunity or a history of drug use, both of which might interfere with thyroid function. Results: After exclusion of samples positive for thyroid antibodies (Antithyroperoxidase; TPOAb, Antithyroglobulin; TgAb), the final sample size for the evaluation of TSH, FT3, and FT4 reference ranges was 509 (254 females, 255 males) and the age range was 15-80 (mean 34.1, median 30). The prevalence of antithyroid antibodies was 17.8% in total and positive thyroid antibodies were more common among females (13.6%) than males (4.2%). We established the reference intervals for the healthy adults as 0.41-4.25 mIU/L for TSH, 0.61-1.06 ng/dL (7.85-13.64 pmol/L) for FT4, and 2.62-3.84 pg/mL (4.02-5.90 pmol/L) for FT3. Conclusion: The reference intervals of thyroid hormones vary considerably from those of other populations and the intervals recommended by the manufacturer. This underlines the need for population-specific reference ranges.

Keywords: Reference intervals, thyroid antibodies, thyrotropin, free thyroxine, free triiodothyronine

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