While pediatric and adolescent thyroid dysfunction can affect many bodily functions, there’s no need to run thyroid labs in all pediatric and adolescent patients, according to a pediatric and adult endocrinologist with Wendy Novak Diabetes Institute, a part of Norton Healthcare and Norton Children’s.

“I don’t recommend routine screening unless I suspect something is going on,” said Lisal J. Folsom, M.D., also an associate professor of pediatrics with an associate appointment in internal medicine at the University of Louisville School of Medicine.

Dr. Folsom presented during a continuing medical education opportunity, “Thyroid: How Much Blame Does It Deserve?”

An enlarged thyroid gland on examination is one reason to consider testing thyroid levels. Any symptoms of hypothyroidism or hyperthyroidism also warrant testing.

Potential signs of hypothyroidism are fatigue, constipation, irregular periods, goiter, a lower-than-expected heart rate, pubertal delay, signs of precocious puberty or poor linear growth.

Fatigue, heat intolerance, diarrhea, goiter, heart palpitations, irregular periods, earlier puberty changes and growth acceleration are symptoms of hyperthyroidism.

Because there are at least 159 different labs that relate to thyroid function, it’s important to focus on those that provide the most relevant answers, according to Dr. Folsom, who practices with Norton Children’s Endocrinology, affiliated with the UofL School of Medicine, and Norton Community Medical Associates – Endocrinology.

Hypothalamic pituitary thyroid hormone feedback loop

This feedback loop, also referred to as the hypothalamic-pituitary-thyroid (HPT) axis, regulates thyroid hormone levels in the body. The hypothalamus produces thyrotropin-releasing hormone (TRH), stimulating the pituitary gland to make thyroid stimulating hormone (TSH), which stimulates the thyroid gland to make thyroid hormone. Most of the thyroid hormone is thyroxine (T4), which is converted to triiodothyronine (T3) in the circulation by thyroid peroxidase (TPO) and other enzymes.

Hypothyroidism

With primary hypothyroidism, the underactive thyroid gland is not producing enough thyroid hormone, which causes the pituitary to increase the amount of TSH. In primary hypothyroidism, a thyroid panel should show elevated TSH and low T4. If the issue lies higher up, in the pituitary gland or hypothalamus, TSH levels could be low, inappropriately normal, or even a little high — because it is not being regulated; T4 likely will be low.

The most common cause of hypothyroidism in the United States is autoimmune hypothyroidism, or Hashimoto thyroiditis, which is also called chronic lymphocytic thyroiditis.

Relevant labs for autoimmune hypothyroidism are TSH, looking at the pituitary, either a total or free T4, and antibodies to both thyroid peroxidase and thyroglobulin to evaluate for an autoimmune cause, according to Dr. Folsom.

Hyperthyroidism

The most common cause of hyperthyroidism is Graves disease, which is caused by thyrotropin receptor antibodies. These bind to the TSH receptor, stimulating thyroid hormone synthesis, but because it is not being stimulated by TSH, there’s no negative feedback.

Graves disease is diagnosed with biochemical testing looking at TSH, T4, total T3 and antibodies specific to Graves disease, which can include TRAb, TSI and TBII. T3 is important to measure, because endogenous hyperthyroidism is more likely to be T3 predominant, according to Dr. Folsom.

Nuclear medicine imaging — using low-dose, radioactive-labeled iodine — also can be useful in the diagnosis of hyperthyroidism by showing thyroid uptake. If nuclear imaging is not available, a thyroid ultrasound with vascular assessment is another possibility. If the gland is highly vascular, that also can indicate a hyperthyroid state.

Toxic nodules are a less-common cause of pediatric hyperthyroidism. These are diagnosed by a finding of elevated thyroid hormone, low TSH and a nodule, either on exam or on imaging. Unlike Graves disease, in which the whole gland “lights up” with nuclear imaging, only one or several nodules do so with toxic nodules.

Hashitoxicosis is another hyperthyroid — overactive thyroid — state. It can be the beginning stage of Hashimoto thyroiditis, which is a form of hypothyroidism.

Hashitoxicosis can be diagnosed by finding elevated thyroid hormone levels in the blood and, unlike the positive TRAb or TSI associated with Graves disease, positive TPO or thyroglobulin antibodies. Another difference between hashitoxicosis and Graves disease: Nuclear medicine uptake scan will show low uptake, because the gland isn’t making thyroid hormone, only releasing stored hormone due to inflammation.

Other causes of abnormal thyroid lab results can be related to stress and illness, including euthyroid sick syndrome (also known as nonthyroidal illness syndrome), which alters the way iodine is added or removed. Biotin is another cause. Biotin is a B-complex vitamin in many hair, nail, and skin vitamins and supplements that interferes with hormone tests.