Facts about thyroid-stimulating hormone (TSH)

Do you have symptoms that suggest that your thyroid is not functioning quite right? Or just want to know more about thyroid health?

Firstly, what is the thyroid gland?
The thyroid gland is a small organ located just under the skin in the neck. This bow tie-shaped organ is usually only about 5 cm across and normally can’t be felt or seen. The thyroid releases specific hormones (chemical messengers) that act on almost every tissue in the body (1).

These thyroid hormones are called thyroxine (T4) and triiodothyronine (T3). T4 and T3 influence a whole range of bodily functions, including skin health, growth, heart rate, fertility, digestion, and weight control.

Normal thyroid hormone levels are very important for a healthy functioning body. But what controls the levels of T4 and T3?

That is where thyroid-stimulating hormone (TSH) comes into the picture. TSH is another hormone, but this one is produced in the pituitary gland, a small gland at the base of the brain. As the name suggests, TSH stimulates the thyroid to produce the T4 and T3 hormones that then go on to act on cells throughout the body (1).

When thyroid hormone levels in the blood are high, the pituitary gland slows the release of TSH, so fewer thyroid hormones are produced. When thyroid hormone levels fall, the pituitary gland speeds up the release of TSH, so it stimulates the thyroid to produce more thyroid hormones (1).

Why measure TSH levels?
TSH levels are usually the best indicator of thyroid function.

If TSH levels are high, it is generally indicative of an underactive thyroid (hypothyroidism), meaning it requires more stimulation (higher TSH) than normal.

If TSH levels are low, it usually indicates an overactive thyroid (hyperthyroidism), which requires less stimulation (lower TSH) than normal.

What are the symptoms of hypothyroidism?
Hypothyroidism means the thyroid is not producing as much T4 and T3 as normal. This effectively slows down functions throughout the body, leading to symptoms such as:

  • Fatigue
  • Puffy eyes and face
  • Slower heart rate
  • Constant feeling of cold
  • Confusion
  • Depression
  • Weight gain
  • Constipation
  • Dry and brittle hair and skin
  • Fertility issues

Treatment options for hypothyroidism include daily medications (e.g. levothyroxine), natural thyroxine hormone extracts, and reduced consumption of substances that affect levothyroxine absorption (2).

What are the symptoms of hyperthyroidism?
Hyperthyroidism means that the thyroid is overproducing T4 and T3. This overproduction speeds up lots of processes in the body, leading to symptoms such as:

  • Fast heart rate
  • High blood pressure
  • Excess sweating
  • Weight loss
  • Anxiety
  • Shaky hands
  • Sleeping issues
  • Increased bowel movements
  • Mood changes

Medication, radioactive iodine, or surgical removal of the thyroid gland are effective treatments for hyperthyroidism (2).

It is important to note that abnormal TSH levels sometimes do not accurately reflect thyroid function. For example, if there is a health issue with the pituitary gland that is interfering with the detection of thyroid hormones in the blood and/or the release of TSH. Additional tests may be required in some instances for an accurate diagnosis. These additional tests can include measuring the levels of T4 and T3, as well as measuring the levels of specific antibodies that are altered in certain health conditions.

Checking the function of your thyroid is simple with a range of tests offered by us. Take our simple Thyroid Stimulating Hormone (TSH) Test for TSH alone, our Thyroid Health Panel to also include T4 and T3 along with TSH, or opt for the Thyroid Health, Complete Panel to also include Anti-Tg and Anti-TPO.

1. Hershnan JM. (Modified Oct 2020). Overview of the Thyroid Gland. Merck Manual Consumer Version
2. Rugge JB, Bougatsos C, & Chou R. (2014) Screening for and Treatment of Thyroid Dysfunction: An Evidence Review for the U.S. Preventive Services Task Force [Internet]. In Evidence Syntheses, No.118. Rockville, MD: Agency for Healthcare Research and Quality (US).