Thyroid Stimulating Hormone
What is TSH?
Thyroid Stimulating Hormone (TSH) is a hormone secreted into the blood by Pituitary gland. TSH signals thyroid gland (a small, butterfly-shaped gland located in front of the neck) to release the thyroid hormones into the blood. The Thyroid Stimulating Hormone (TSH) Test measures the levels of TSH in the blood.
Why is TSH done?
To diagnose any suspected thyroid diseases (Hypothyroidism or Hyperthyroidism)
To monitor the effect of treatment in patients with thyroid diseases, e.g. in case of hypothyroid patients receiving various thyroid hormone preparations: Low values are found in states of high doses
To screen for any thyroid diseases during pregnancy
To screen for any thyroid diseases in newborns
What does TSH Measure?
Thyroid Stimulating Hormone (TSH) test measures the amount of TSH in your blood which helps to find out if the thyroid gland is working normally or not. Low TSH levels indicate hyperthyroidism and high TSH levels indicate hypothyroidism.
In case of hyperthyroidism, the thyroid gland produces very high amounts of thyroid hormones (T3 and T4) and you may experience symptoms of weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity towards heat, etc. In case of Hypothyroidism, there is a decrease in the production of thyroid hormones (T3 and T4) which may cause weight gain, fatigue, slow heart rate, increased sensitivity towards cold, depression, dry and thin hair, etc.
There is a feedback system in the body to maintain stable amounts of the thyroid hormones (T3 and T4) in the blood. TSH signals the thyroid gland to make and release the thyroid hormones (T3 & T4) into the blood when the level of thyroid hormones is low and can also signal the thyroid gland to lower the production of thyroid hormones when the level of thyroid hormones is very high. So, when the thyroid hormone (T3 and T4) levels decrease, the pituitary gland is stimulated to release TSH and this high TSH level, in turn, stimulates thyroid gland to release more thyroid hormone (T3 & T4) from the thyroid gland and the vice-versa happens when the thyroid hormone levels are very high.
Interpreting TSH results
The TSH normal range may vary from lab to lab.
The TSH normal range for different age groups is given below:
Patients (Age) TSH Normal Range
Premature Infants (28-36 Weeks)
1st Week of Life
Term Infants (>37 Weeks)
Serum or Cord Blood
5 Days-4 Weeks
- If your TSH level is increased, it usually indicates that you have hypothyroidism. Hashimoto’s thyroiditis is the most common cause of primary hypothyroidism.
- If your TSH level is decreased, it usually indicates hyperthyroidism. Graves' disease, multinodular goiter, toxic nodule are some of the common causes of hyperthyroidism.
Note: TSH normal range levels show circadian variation (fluctuates during the 24-hour cycle), reaching peak levels between 2-4 am and are at a low between 6-10 pm.