TSH stands for thyroid-stimulating hormone. TSH levels, measured with simple blood test, help diagnose thyroid disorders. Scroll down to explore the relationship between thyroid-stimulating hormone and the hormones secreted by thyroid gland.
Thyroid-stimulating hormone (TSH) is a peptide hormone released by the anterior pituitary gland. It stimulates the thyroid gland to release the hormones T3 and T4. The hormone ‘thyrotropin’ released by the hypothalamus regulates the function of the anterior pituitary gland and controls the production of TSH. The hypothalamus also releases the hormone ‘somatostatin’, which acts as the antagonist of ‘thyrotropin’. The imbalance of these antagonistic hormones affects TSH levels in blood.
Functioning of Thyroid and Levels of TSH
Thyroid gland is an important gland in human body. Impaired or excessive production of thyroid hormones can lead to serious health problems. Thyroid gland produces hormones triiodothyronine (also called T3) and thyroxine (also called T4). The release of T3 and T4 is regulated by TSH. There is a typical relationship between the TSH levels and the functioning of the thyroid gland. The production of TSH is inversely proportional to the production of T3 and T4. In case of elevated T3 and T4 levels (due to hyperactive thyroid), pituitary gland restricts the production of TSH and releases less TSH. When the thyroid gland is not able to do its job (when the thyroid is underactive), T3 and T4 levels drop down. In such cases, pituitary gland produces more TSH to stimulate the thyroid. A TSH blood test helps measure the levels of TSH and also provides information about T3 and T4 levels. Take a look at the following chart.
Hormones Released by Thyroid and TSH Levels
| Hormones | Normal Value (mIU/L) | Values Indicating Health Problem | |
| T3 (Serum triiodothyronine) | 80 – 220 | T3 < 80 | Hypothyroidism |
| Free T3 | 2.3 to 4.2 | Free T3 < 2.3 | Hypothyroidism |
| Total T4 (Serum thyroxine) | 4.5 to 12.5 | T4 < 4.5 with elevated TSH | Underactive thyroid |
| T4 > 12.5 | Hyperthyroidism | ||
| T4 < 4.5 with low TSH | Pituitary problem | ||
| Free T4 | 0.7 to 2.0 | Free T4 < 0.7 | Hypothyroidism |
| TSH | 0.3 to 3.0 (as of 2003, revised by the American Association of Clinical Endocrinologists). Still, the reference value may vary according to the labs or doctors. | TSH < 0.3 | Hyperthyroidism |
| TSH > 3.0 | Hypothyroidism | ||
The following chart explains the variations in the levels of TSH and thyroid status.
Levels of TSH and Thyroid Health
| Description | TSH Count |
| Normal Levels of TSH | 0.4 – 4.0 mIU/L |
| Underactive Thyroid | 2.0 mIU/L or more |
| Thyroid Disorder | 0.5 and 3.0 mIU/L |
Here, mIU/L stands for milli-international units per liter. Normal thyroid levels may vary from person to person. Labs use 0.4 – 5.0 mIU/mL as the reference range for TSH for adults. The normal TSH level for children can be slightly higher than the adults. Here are the effects of low and high thyroid levels on the body.
Underactive Thyroid
Low thyroid levels result in low basal metabolic rate. The main symptoms can be loss of appetite and increased fatigue. If you are experiencing increased sleepiness all the time or frequent attacks of cold, you should check your TSH and thyroid hormone levels. Joint pain, swelling in the neck, dry skin, hair loss, hoarse voice, difficulty in controlling cholesterol levels in spite of following a proper diet, are some other symptoms of a sluggish thyroid.
Overactive Thyroid
The symptoms of an overactive thyroid (hyperthyroidism) include irregular heartbeats, hot flashes, nervousness resulting in depression, confusion or poor concentration and weight loss. Women may experience joint pain and irregular menstrual cycles. Hyperthyroidism in men can lead to impotence or rapid heart rate. Some patients may experience symptoms such as increased bowel movement, heat intolerance, palpitations, arrhythmia, profuse sweating, increased irritability, decreased concentration, weight loss, tremor, or insomnia. To diagnose thyroid problems, doctors need the values of TSH along with the values of T3 and T4. Simultaneous measurement of T3, T4, and TSH count helps detect the cause of abnormal functioning of thyroid gland.
Though the thyroid levels might fluctuate sometimes, seek medical help if you notice any of the aforementioned symptoms. A simple blood test can help you find out T3, T4, and TSH levels. Doctors usually prescribe medicines and stress on the need to follow certain dietary guidelines, in case of people affected by thyroid disorder. The diet helps manage the symptoms naturally. Everyone knows that including the element iodine in diet helps maintain thyroid levels. Follow-up tests would be required in case of people diagnosed with thyroid cancer.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.
