title: Raised serum TSH levels in patients with morbid obesity: is it enough to diagnose subclinical hypothyroidism?
abstract: OBJECTIVE
  Morbid obesity (body mass index (BMI)> or =40 kg/m(2)) is associated with thyroid function disturbances, with a high rate of subclinical hypothyroidism (SH) being the most consistently reported. We evaluated the circulating thyroid function parameters in morbid obese patients and related the results to the presence of circulating thyroid antibodies (Thyr-Ab).
  
  
  METHODS
  Morbid obese patients were consecutively enrolled (n=350). Two control groups were used: control group (CG)1, healthy normo-weight subjects (n=50); CG2, normo-weight patients with SH (n=56) matched for TSH with the obese patients with SH. Serum levels of free triiodothyronine (FT(3)), free thyroxine (FT(4)), TSH, antithyroglobulin antibodies, and antithyroperoxidase antibodies were measured in all patients.
  
  
  RESULTS
  i) Compared with CG1, obese patients having thyroid function parameters in the normal range and negative Thyr-Ab showed significantly higher serum TSH and lower free thyroid hormones levels, but a similar FT(4)/FT(3) ratio; ii) SH was recorded in 13.7% obese patients; iii) compared with CG2, obese patients with untreated SH had a significantly lower rate of positive Thyr-Ab (32.1 vs 66.1%; P<0.005); iv) no gender prevalence was observed in SH obese patients with negative Thyr-Ab; and v) the comparison of the untreated SH patients (obese and normo-weight) with CG1 demonstrated that in SH obese subjects, unlike normo-weight SH patients, the FT(3) levels were significantly lower. This resulted in a normal FT(4)/FT(3) ratio in SH obese patients.
  
  
  CONCLUSIONS
  Thyroid autoimmunity is not a major cause sustaining the high rate of SH in morbid obese patients. In these patients, the diagnosis of SH itself, as assessed by a raised TSH alone, appears questionable.
authors.affiliation: Unit of Internal Medicine and Endocrinology, Fondazione Salvatore Maugeri IRCCS, ISPESL Laboratory for Endocrine Disruptors, Chair of Endocrinology, University of Pavia, Pavia, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Rotondi
authors.forename: Paola
authors.initials: P
authors.lastname: Leporati
authors.forename: Antonella
authors.initials: A
authors.lastname: La Manna
authors.forename: Barbara
authors.initials: B
authors.lastname: Pirali
authors.forename: Teresa
authors.initials: T
authors.lastname: Mondello
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Fonte
authors.forename: Flavia
authors.initials: F
authors.lastname: Magri
authors.forename: Luca
authors.initials: L
authors.lastname: Chiovato
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000097:blood; D015415:Biomarkers / Q000097:blood; D001835:Body Weight; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000175:diagnosis / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000097:blood* / Q000453:epidemiology*; D009195:Peroxidase / Q000276:immunology; D011237:Predictive Value of Tests; D015995:Prevalence; D013967:Thyroiditis, Autoimmune / Q000097:blood / Q000150:complications / Q000175:diagnosis; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; C006606:anti-thyroglobulin; D014284:Triiodothyronine; D013972:Thyrotropin; D009195:Peroxidase; D013974:Thyroxine