The thyroid stimulating hormone or thyrotropin (TSH) It is responsible for the thyroid releasing its hormones, something that has a key role in our metabolism. High TSH levels generally indicate hypothyroidism, while low TSH levels are a sign of hyperthyroidism. We explain to you what are normal TSH levels by age and When to worry about high or low numbers.

What is TSH and what is its function?

TSH is a hormone produced by the pituitary gland in the brain. Its main function is to tell the thyroid gland to produce and release thyroid hormones to the blood

It therefore acts on the thyroid gland to stimulate the production of thyroxine (T4) and triiodothyronine (T3)which are essential to maintain the body metabolic rate (the speed at which it transforms food into energy and uses it) and for various physiological processes in the body.

Normal TSH values ​​by age

The TSH test, which measures the levels of this hormone, is used to find out if the thyroid gland is working properly and to detect a thyroid disorder before the first symptoms appear.

The Normal TSH levels in adults are usually between 0.4 and 4.0 milliunits per liter (mU/L), according to the American Thyroid Association (American Thyroid Association), although there are organizations and laboratories that consider that the upper limit may be higher (between 4 and 5). These levels vary greatly depending on age and, according to the Cleveland Clinic, they are:

• Babies up to 5 days: 0.7 – 15.2 mU/l.
• Infants from 6 to 90 days: 0.72 – 11.0 mU/l.
• Babies from 4 to 12 months: 0.73 – 8.35 mU/l.
• Children from 1 to 6 years: 0.7 – 5.97 mU/l.
• Children from 7 to 11 years: 0.6 – 4.84 mU/l.
• People from 12 to 20 years old: 0.51 – 4.3 mU/l.
• Adults from 21 to 99 years old: 0.27 – 4.2 mU/l.

These levels may vary in specific groups such as pregnant women or people with certain diseases.

What it means to have high TSH

Some TSH levels above normal indicate that the thyroid gland is not producing enough thyroid hormones, that is, there is hypothyroidism. When the thyroid gland does not produce enough thyroid hormones, the pituitary gland releases more TSH in an attempt to stimulate the thyroid to produce more hormones.

The hypothyroidism symptoms They include tiredness, weight gain, constipation, dry skin, hair loss, sensitivity to cold, muscle weakness, memory problems, menstrual problems, swelling of the face, hands or feet, and depression. However, the TSH levels may be high before these symptoms occur.

The severity of hypothyroidism It can be classified according to TSH levels as: mild (TSH between 4.0 and 10.0 mU/L), moderate (TSH between 10.0 and 20.0 mU/L) or severe (TSH greater than 20.0 mU/L).

The causes of high TSH levels They can be a deficiency or excess of iodine, autoimmune thyroid diseases (such as Hashimoto’s thyroiditis), the use of certain medications, congenital hypothyroidism, whether the person is undergoing radiotherapy or a disorder of the pituitary gland.

What it means to have low TSH

Some low TSH levels They generally indicate that the thyroid gland is overactive and therefore there is hyperthyroidism. The thyroid produces excessive amounts of thyroid hormones (T4 and T3), leading to suppression of TSH levels.

The symptoms of hyperthyroidism They include weight loss or increased appetite, rapid heartbeat (palpitations), anxiety, mood changes or irritability, menstrual irregularities, heat intolerance, sleep disorders, bulging eyes, shaking, and sweating.

The most common cause of hyperthyroidism is an autoimmune disorder called Graves’ disease, in which the immune system mistakenly attacks the thyroid gland. Other causes include thyroid nodules, thyroiditis (inflammation of the thyroid), the use of certain medications, and rare diseases such as toxic adenoma or thyroid cancer.