Obesity and Thyroid Function Tests in Children
Larry A. Fox, MD
Nemours Children’s Health
Jacksonville, Florida
September 22, 2021
Background
Pediatricians and other practitioners are regularly faced with ordering thyroid function tests (TFTs) in children for a variety of clinical reasons. Sometimes it is a child displaying symptoms suggesting hypothyroidism, development of a goiter, or a decline in growth velocity. It is also common for physicians to order TFTs because the patient is obese, and quite often these thyroid labs are abnormal. With the epidemic of childhood obesity, our clinic is seeing an increasing number of referrals for abnormal TFTs in the setting of obesity. It is important for pediatricians to understand how TFTs are affected by obesity, when thyroid function tests should be ordered, and when a referral is necessary.
The relationship between thyroid function tests and obesity
The effect obesity has on thyroid function has been well documented in adults and children. In most studies, TSH is proportional to BMI. TSH results may be within the assay reference range, but are often slightly above. Thus, it is quite common for obese children (and adults) to have elevated TSH (with slightly increased free or total T3 and normal free T4), suggesting compensated hypothyroidism. In fact, TSH levels are above the reference range in up to 25% of obese children, and several population studies suggest TSH reference ranges need to be adjusted for obesity. Changes in TSH are thought to be mediated by increased leptin causing an increased pituitary release of thyrotropin releasing hormone and a rise in TSH. These changes increase resting energy expenditure and thus are adaptive to the obesity. They do not cause the obesity as evidenced by a decline in TSH with weight loss, either with bariatric surgery (in adults) or lifestyle changes in children and adults.
When should thyroid functions tests be done in an obese child?
Under many clinical circumstances checking TFTs (TSH, free T4) in the setting of obesity is reasonable, such as poor growth, goiter, and/or more specific symptoms suggesting hypothyroidism (such as cold intolerance, generalized dry skin, fatigue or constipation). Simply being overweight or obese (BMI >85th or >95th percentile, respectively) are not symptoms of hypothyroidism and ordering TFTs would not be indicated. Obtaining TFTs in overweight or obese patients without clear indications could lead to unnecessary additional testing, treatment, or referrals. Because the TFT changes are adaptive and do not cause the obesity, treatment is thought not to be necessary.
What should one do if the TSH is abnormal?
If the TSH is elevated above the reference range in an obese individual, the practitioner must decide whether further testing, treatment and/or referral is needed. Because autoimmune disorders are more common in obese individuals, it is reasonable to obtain markers of autoimmune (Hashimoto) thyroiditis (i.e., thyroid peroxidase and thyroglobulin antibody titers). If antibody titers are elevated, referral to a thyroid specialist is reasonable. If the child has a goiter or a nodule is palpable, a thyroid ultrasound would also be informative. If the ultrasound reveals a nodule or cyst, the patient should be referred to a thyroid specialist.
Otherwise, mild elevations in TSH without a goiter do not need treatment and a referral would not be necessary. Instead, rechecking TSH and free T4 in 3-6 months to document the trend in TFTs indicated.
Conclusion
TFTs are commonly abnormal in obese patients, with serum TSH concentrations often above the reference range. These laboratory abnormalities are due to changes in leptin and reflect an adaptation to obesity. Most often the abnormal TFTs do not require treatment. In some circumstances, however, a referral to a thyroid specialist is warranted.
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