Natural course of euthyroidism and clues for early diagnosis of thyroid dysfunctions: Tehran Thyroid Study (TTS).

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Natural course of euthyroidism and clues for early diagnosis of thyroid dysfunctions: Tehran Thyroid Study (TTS).

Thyroid. 2017 Jan 10;:

Authors: Amouzegar A, Ghaemmaghami Z, Beygi M, Gharibzadeh S, Mehran L, Tohidi M, Azizi F

Abstract
OBJECTIVE: 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.
METHODS: This study was conducted within the framework of the Tehran Thyroid cohort study (TTS), in which 5783 individuals aged 40.4 ± 0.2 years were followed for 6 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 (TFT), clinical, and metabolic characteristics were assessed at baseline and every 3 years.
RESULTS: The annual incidence rates (95% CIs) of subclinical and overt hypothyroidism were 7.62 (7.39-7.85) and 2.0 (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 dysfunctions were TSH, FT4 and TPOAb levels, gender, 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 TFTs and TPOAb. Early diagnosis of hypothyroidism was significantly attributed to impaired glucose tolerance (relative risk with 95% CIs 3.03, 1.36-6.75; p = 0.007), high cholesterol (relative risk with 95% CIs 2.46, 1.45-4.18; p = 0.001), obesity (relative risk with 95% CIs 2.92, 1.64-5.2; p < 0.001), and hypertension (Relative risk with 95% CIs 1.68, 1.53-1.84; p <0.04).
CONCLUSION: This study showed that after a six-year follow-up in an iodine sufficient area, 6.7% of euthyroid subjects were found to progress to thyroid dysfunctions, subclinical hypothyroidism in particular.

PMID: 28071990 [PubMed - as supplied by publisher]

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