Prevalence of hypothyroidism in patients with dyslipidemia: Tehran Thyroid Study (TTS).

Hypothyroidism is a relatively common endocrine disorder usually accompanied with changes in serum lipid profiles. The purpose of this study was to assess the association between dyslipidemia and hypothyroidism in a population-based study. In this cross-sectional study, 2,315 dyslipidemic patients, aged 20-90 years (mean age: 38.1 ± 13.2 years), were selected from among 5,760 participants of Tehran Thyroid Study and divided into 3 groups, the subclinical hypothyroid, overt hypothyroid, and euthyroid subjects, based on national reference ranges. Serum lipid profiles, free thyroxine (FT4), thyroid stimulating hormone (TSH), and thyroid peroxidase antibody (TPOAb) were measured in all subjects. In subjects with dyslipidemia and nondyslipidemia, the prevalence of subclinical was 7% and 4.1%, respectively, and for clinical hypothyroidism 3% and 1.2%, respectively. In dyslipidemic subjects, the mean low density lipoprotein-cholesterol (LDL-C) levels differed significantly (p = 0.03) among the overt hypothyroid (144.3 ± 36.1), subclinical hypothyroid (129.3 ± 39.2), and euthyroid (132.7 ± 39.0) groups. In the overt hypothyroid group, mean total cholesterol level was higher than in the normal group, but not significant. There were no differences in median triglycerides (TG) and mean high density lipoprotein-cholesterol (HDL-C) levels among the 3 groups mentioned. After adjusting for age and sex, hypothyroidism was not related to elevated serum lipid profiles in patient with dyslipidemia. In conclusion, there is significant difference in the prevalence of subclinical and clinical hypothyroidism between nondyslipidemic and dyslipidemic subjects; after adjustment for age and sex the presence of dyslipidemia did not predict the presence of hypothyroidism.

Local versus international recommended TSH references in the assessment of thyroid function during pregnancy.

The aim of this study was to compare the prevalence of subclinical and overt hypothyroidism based on local population-specific reference intervals versus arbitrary cutoffs that are not specific for the population studied or the assay used, during pregnancy in an area of iodine sufficiency. We tested a total of 203 pregnant women in the first trimester of pregnancy, and followed their status in the second and third trimesters. Serum samples from women were assayed for levels of total T4 and T3, FT4I, TSH, TPOAb, and TgAb. Of the 203 women based on our national trimester specific reference ranges of serum TSH and FT4I, 153, 157, and 157 were euthyroid in 3 consecutive trimesters of pregnancy. Accordingly, a total of 23, 12, and 13 had subclinical hypothyroidism in the first, second, and third trimester, respectively. Overt hypothyroidism was detected in 4, 5, and 1 women in the first, second, and third trimesters of pregnancy, respectively. The prevalence of subclinical hypothyroidism was 49, 31, and 34 in each of the trimesters respectively, when TSH>2.5 mIU/l was considered for definition of hypothyroidism in the first trimester, and over 3 mIU/l in the second and third trimesters. Our results showed that using arbitrary cutoff values for TSH instead of population-specific reference intervals may inappropriately increase the rate of subclinical hypothyroidism.

An assessment of the iodine status and the correlation between iodine nutrition and thyroid function during pregnancy in an iodine sufficient area.

BACKGROUND: Iodine as a micronutrient is mandatory for thyroid hormone production and inadequate iodine intakes during pregnancy may result in varying degrees of hypothyroidism affecting pregnancy outcomes adversely. The aim of this study was to evaluate nutritional status and its effects on thyroid function in pregnant women during all trimesters of pregnancy. SUBJECTS/METHODS: In this cohort study, we assessed a total of 203 pregnant women in the first trimester of pregnancy and followed them in the second and third trimesters. They were divided into two groups, group I with urinary iodine excretion (UIE) < 150 µg/l, and group II with UIE ≥ 150 µg/l. Serum samples from women were assayed for levels of total T4, T3, FT4I and thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) only once in each trimester. Urinary iodine concentration was measured three times and the median was considered as UIE in the first trimester, but it was measured only once in the second and third trimesters. RESULTS: The median inter quartile ranges of urinary iodine were 218 (150-276) µg/l, 160 (106-260) µg/l and 145 (88-225) µg/l in the three trimesters of pregnancy, respectively; UIE<150 was observed in 48 (24.1%), 90 (44.8%) and 103 (52.3%) of pregnant women in the three trimesters of pregnancy, respectively. The median (range) of TSH was 1.7 (0.9-2.7) mIU/l, 1.9(1.2-2.7) mIU/l and 1.8 (1.1-2.8) mIU/l in the three trimesters of pregnancy, respectively. There was no correlation between UIE, TSH, TT4, FT4I, T3 and TPOAb in the first and second trimesters, but there was a weak correlation between UIE, TSH, T3 and TgAb in the third trimester. CONCLUSION: In our cohort of pregnant women the iodine intakes were sufficient, and no correlation between urinary iodine concentration and thyroid function tests was found.