title: Natural Course of Euthyroidism and Clues for Early Diagnosis of Thyroid Dysfunction: Tehran Thyroid Study.
abstract: Considering the limited data available on the natural course of euthyroidism, this study was designed to evaluate the progression in time from euthyroidism to subclinical or overt hypo- or hyperthyroidism.
  
  
  
  This study was conducted within the framework of the Tehran Thyroid Cohort Study, in which 5783 individuals aged 40.4 ± 0.2 years were followed for six years. The overall loss to follow-up rate was 8.3%. After applying exclusion criteria, data of 4204 euthyroid subjects remained for analysis of a six-year natural course analysis. Thyroid function tests, clinical characteristics, and metabolic characteristics were assessed at baseline and every three years.
  
  
  
  The annual incidence rates [confidence intervals (CI)] of subclinical and overt hypothyroidism were 7.62 [CI 7.39-7.85) and 2.0 [CI 1.94-2.06] per 1000 persons, respectively. For thyroid hyperfunction, the annual incidence rates of subclinical and overt hyperthyroidism were 0.92 [0.90-0.95) and 0.68 [0.66-0.70) per 1000 persons, respectively. Euthyroid persistency was 93.24% during 6 years. Predictive factors for conversion to thyroid dysfunction were thyrotropin, free thyroxine and thyroid peroxidase antibody levels, sex, and smoking. Criteria for early diagnosis of hypothyroidism (i.e., sensitivity of 94% and specificity of 82%, p < 0.0001) were obtained based on baseline and three-year follow-ups of thyroid function tests and thyroid peroxidase antibody. Early diagnosis of hypothyroidism was significantly associated with impaired glucose tolerance (relative risk with 3.03 [CI 1.36-6.75]; p = 0.007), high cholesterol (relative risk 2.46 [CI 1.45-4.18]; p = 0.001), obesity (relative risk 2.92 [CI 1.64-5.2]; p < 0.001), and hypertension (relative risk 1.68 [CI 1.53-1.84]; p < 0.04).
  
  
  
  This study shows that after a six-year follow-up in an iodine sufficient area, 6.7% of euthyroid subjects were found to progress to thyroid dysfunction, in particular subclinical hypothyroidism.
authors.affiliation: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .
authors.forename: Atieh
authors.initials: A
authors.lastname: Amouzegar
authors.affiliation: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .
authors.forename: Zahra
authors.initials: Z
authors.lastname: Ghaemmaghami
authors.affiliation: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .|2 Students Scientific Research Center, Tehran University of Medical Sciences , Tehran, Iran .
authors.forename: Maani
authors.initials: M
authors.lastname: Beigy
authors.affiliation: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .|3 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences , Tehran, Iran .
authors.forename: Safoora
authors.initials: S
authors.lastname: Gharibzadeh
authors.affiliation: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .
authors.forename: Ladan
authors.initials: L
authors.lastname: Mehran
authors.affiliation: 4 Prevention of Metabolic Disorders Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .
authors.forename: Maryam
authors.initials: M
authors.lastname: Tohidi
authors.affiliation: 1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .
authors.forename: Fereidoun
authors.initials: F
authors.lastname: Azizi
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000097:blood; D018450:Disease Progression; D042241:Early Diagnosis; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007453:Iodide Peroxidase / Q000276:immunology; D007492:Iran; D008297:Male; D008875:Middle Aged; D013959:Thyroid Diseases / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*
chemical_list: D001323:Autoantibodies; D013972:Thyrotropin; D007453:Iodide Peroxidase; D013974:Thyroxine
keywords: Tehran Thyroid Study; euthyroid; natural course; thyroid diseases; thyroid function tests