title: The incidence of thyroid function abnormalities and natural course of subclinical thyroid disorders, Tehran, I.R. Iran.
abstract: BACKGROUND
  Despite the high prevalence of thyroid dysfunction, the epidemiology and natural course of these disorders have not been identified yet.
  
  
  OBJECTIVE
  The present survey was conducted to determine the incidence of thyroid dysfunction and natural course of subclinical thyroid disorders in an urban community of Tehran, I.R. Iran.
  
  
  METHODS
  Serum TSH and thyroperoxidase antibody (TPOAb) were measured at baseline and after 6.7 yr from a sample of 1999 randomly selected subjects aged≥20 yr, participants of the Tehran Lipid and Glucose Study (TLGS). Median TSH value and 2.5, 5, 95, and 97.5 TSH percentiles were determined at baseline using data obtained from 808 negative TPOAb subjects with no history of any thyroid disease or surgery, goiter, nodule, taking thyroid hormone preparations or anti-thyroid drugs. In those with abnormal TSH level, total T4 and T3 uptake were measured and free T4 index was calculated.
  
  
  RESULTS
  Normal TSH reference range was 0.4-5.8 μU/ml according to the 2.5 and 97.5 TSH percentiles. The incidence rates of thyroid function abnormalities in 1000 subjects per year were as follows: clinical hypothyroidism: 0.28 in women and 0.21 in men; subclinical hypothyroidism: 11.59 in women and 4.69 in men; clinical hyperthyroidism: 1.4 in women and 0.21 in men; and subclinical hyperthyroidism: 5.72 in women and 3.62 in men. A significant increase was found in the frequency of positive TPOAb in women from 15.9 to 17.7% (p=0.006). Of 8 women with subclinical hypothyroidism at baseline, 5 remained unchanged, 1 became normal, and 1 developed clinical hypothyroidism at followup. Two women with subclinical hyperthyroidism normalized at follow-up. Of 2 men with subclinical hypothyroidism at baseline, 1 remained unchanged, whereas the other progressed to clinical hypothyroidism.
  
  
  CONCLUSIONS
  After a 6.7 yr follow-up significant increase in the incidence of subclinical thyroid disorders was observed in both men and women, as compared to overt thyroid dysfunction. Increase in the prevalence of TPOAb positivity was observed only in women.
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, P.O. Box: 19395-4763, Tehran, I.R. Iran.
authors.forename: H
authors.initials: H
authors.lastname: Delshad
authors.forename: L
authors.initials: L
authors.lastname: Mehran
authors.forename: M
authors.initials: M
authors.lastname: Tohidi
authors.forename: M
authors.initials: M
authors.lastname: Assadi
authors.forename: F
authors.initials: F
authors.lastname: Azizi
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000097:blood; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007453:Iodide Peroxidase / Q000097:blood; D007492:Iran / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D013959:Thyroid Diseases / Q000097:blood / Q000453:epidemiology* / Q000473:pathology*; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D014284:Triiodothyronine; D013972:Thyrotropin; D007453:Iodide Peroxidase; D013974:Thyroxine