Session: SAT 622-631-Pediatric Endocrinology: Thyroid
Poster Board SAT-626
Subclinical hypothyroidism (SCH) is defined by a mild elevation in serum TSH but normal serum free T4 (FT4). It is a common condition among children, particularly among those who are overweight or obese, and is a frequent cause for referral to pediatric endocrinology clinics. Hypothyroidism has been associated with both iodine deficiency and iodine excess. Our objective was to determine iodine status in a multiethnic cohort of children with idiopathic SCH.
Design and methods:
In this prospective study, patients were ascertained among those referred to the Pediatric Endocrinology Clinic at the University of Miami for evaluation of an abnormally elevated TSH. Subjects were recruited if they had a serum TSH between 5 and 15 mIU/L, normal free T4 and absence of anti-thyroid antibodies. Subjects with other endocrine disorders or systemic illness were excluded. None of the subjects was taking an iodine-containing medication. Twenty-four hour urinary iodine and creatinine were determined to assess iodine status. Subjects were excluded if the 24-hour urinary creatinine excretion was markedly low.
Seventeen subjects (8 males and 9 females) were enrolled into the study. Subjects were 6-18 years old (mean ± 1SD: 10.9 years ± 3.5 years). Mean FT4 was 1.13±0.12 ng/dl. Serum TSH was 7.27±2.35 mIU/L. Two subjects were considered iodine deficient (24 hour urinary iodine <100 mcg/L) whereas four subjects had abnormally high iodine levels (urinary iodine >300 mcg/L).
Nearly one third of subjects with idiopathic SCH we studied had abnormal iodine status. The prevalence of iodine deficiency was lower than that of the general population (12% in our study versus 20% from NHANES data) but it is possible that low iodine intake was the cause of the SCH in the two patients with subnormal iodine intake that we identified. Our data indicated that a relatively large number of subjects with SCH had iodine excess. This finding was unexpected. We cannot be sure that the SCH in these 4 of 17 subjects was caused by the iodine excess, but the data suggest the importance of larger studies to investigate iodine excess as a cause of mild elevation of TSH in apparently normal subjects with idiopathic SCH.
Nothing to Disclose: SG, AM, TS
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