Prevalence, clinical and biochemical profile of subclinical hypothyroidism in normal population in Mumbai

BACKGROUND: Subclinical Hypothyroidism (ScHt) affects 3-15% of the adult population. It's clinical and biochemical profile is not well defined, especially in Indian scenario. Our study aimed at screening normal population to define normative ranges of thyroid hormones and Serum thyroid stimulating hormone (S.TSH) and prevalence of ScHt and thyroid autoimmunity. MATERIALS AND METHODS: Two-hundred thirty-seven normal subjects without family history of thyroid disease were evaluated for symptoms and laboratory tests for thyroid dysfunction and autoimmunity. RESULTS: The thyroid function tests were as follows: EUTHYROID GROUP: MEAN VALUES WERE: T3: 1.79 ± 0.42 ng/mL, T4: 10.23 ± 2.25 μg/dL, FT3: 1.88 ± 0.19 pg/mL, FT4: 1.12 ± 0.21 ng/dL, S.TSH: 2.22 ± 1.06 μlu/mL. 10.2% of euthyroid subjects had antimicrosomal antibodies (AMA) +ve (mean titer 1:918) and 23.6% were anti-thyroid peroxidase autoantibody (anti-TPO) +ve (mean titer 15.06 Au/mL). The euthyroid outlier range for S.TSH was 0.3-4.6 μlu/mL. The values were comparable in both the sexes. Those with S.TSH ≥ 5 μlu/mL were defined to have ScHt. SCHT GROUP: Prevalence of ScHt was 11.3% (M:F ratio 1:3.7). 74% belonged to 35-54 years age group and prevalence increased with age (post-menopausal females: prevalence 20%). S.TSH was 9.8 ± 7.22 μlu/mL, mean S.AMA was 1:5079 (40.7% positivity) and mean S.anti-TPO was 260 Au/mL (47.6% positivity). Majority were agoitrous (74%), and stage I goiter was seen in 26% of this population. Symptom score of 5-8 was seen in 55% ScHt subjects versus 35% normal subjects. CONCLUSION: Mean S.TSH in our population was 2.22 μlu/mL (euthyroid outliers: 0.3-4.6 μlu/mL); hence, S.TSH above 4.6 μlu/mL should be considered as abnormal. The prevalence of thyroid autoimmunity increases after age of 35 years. ScHt presents mainly in agoitrous form and with positive antibodies, suggesting autoimmunity as the cause.