title: Free triiodothyronine/free thyroxine ratio rather than thyrotropin is more associated with metabolic parameters in healthy euthyroid adult subjects.
abstract: OBJECTIVE
  The interrelation between TSH, thyroid hormones and metabolic parameters is complex and has not been confirmed. This study aimed to determine the association of TSH and thyroid hormones in euthyroid subjects and the relationship between thyroid function and metabolic risk factors. Furthermore, this study examined whether thyroid function has predictive power for metabolic syndrome.
  
  
  METHODS
  This is a cross-sectional study that included subjects in a medical health check-up programme at a single institution.
  
  
  METHODS
  The study included 132 346 participants (66 991 men and 65 355 women) aged over 18 years who had TSH, free T4 (FT4) and free T3 (FT3) levels within the institutional reference ranges.
  
  
  METHODS
  Thyrotropin, FT4, FT3 and metabolic parameters including height, weight, waist circumference, blood pressure, serum levels of total cholesterol, triglyceride, high-density lipoprotein cholesterol, insulin and glucose were measured.
  
  
  RESULTS
  There was a positive association between FT3/FT4 ratio and TSH in both men and women after adjusting for age, body mass index, smoking status and menopausal status (in women). The FT3/FT4 ratio and TSH were positively associated with risk of metabolic syndrome parameters including insulin resistance. The FT3/FT4 ratio had a greater predictive power than TSH for metabolic syndrome in both men and women.
  
  
  CONCLUSIONS
  Thyrotropin levels were positively associated with FT3/FT4 ratio within the euthyroid range. The higher FT3/FT4 ratio is associated with increased risk of metabolic syndrome parameters and insulin resistance. FT3/FT4 ratio has a better predictive power for metabolic syndrome than TSH.
authors.affiliation: Department of Internal Medicine, Cheil General Hospital, Dankook University College of Medicine, Seoul, Korea.
authors.forename: So Young
authors.initials: SY
authors.lastname: Park
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Se Eun
authors.initials: SE
authors.lastname: Park
authors.affiliation: Department of Internal Medicine and Laboratory of Genomics and Translational Medicine, Gachon University School of Medicine, Incheon, Korea.
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Jung
authors.affiliation: Department of Biomedical Laboratory Science, College of Life and Health Sciences, Hoseo University, Asan, Korea.
authors.forename: Hyun Seok
authors.initials: HS
authors.lastname: Jin
authors.affiliation: Department of Internal Medicine and Laboratory of Genomics and Translational Medicine, Gachon University School of Medicine, Incheon, Korea.
authors.forename: Ie Byung
authors.initials: IB
authors.lastname: Park
authors.affiliation: Department of Preventive Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.
authors.forename: Song Vogue
authors.initials: SV
authors.lastname: Ahn
authors.affiliation: Department of Internal Medicine and Laboratory of Genomics and Translational Medicine, Gachon University School of Medicine, Incheon, Korea.
authors.forename: Sihoon
authors.identifier: http://orcid.org/0000-0002-9444-5849
authors.initials: S
authors.lastname: Lee
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood / Q000175:diagnosis*; D055442:Metabolome; D008875:Middle Aged; D011237:Predictive Value of Tests; D012307:Risk Factors; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D055815:Young Adult
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine
keywords: FT3/FT4 ratio; TSH; metabolic syndrome; thyroid hormone