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TSH test

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What is a TSH test?

The TSH test or the thyroid stimulating test is the first test that is ordered when any kind of thyroid disease is suspected. The thyroid functions under a complex system of checks and balances wherein the release of its hormones is controlled by the hypothalamus and the pituitary gland.

TSH is released by the pituitary gland when prompted by TRH or thyrotropin releasing hormone released by the hypothalamus. In turn, TSH prompts the thyroid to produce and release T4 and T3 in the blood. Thus, its main role is to control and regulate the functioning of the thyroid gland. Though this hormone is not released by the thyroid itself, its level in the bloodstream gives a clear indication of any kind of disturbances related either to the thyroid or the pituitary gland.

Why is it conducted?

Thyroid disease is very common and often escapes notice as its symptoms are very similar to other disorders. The TSH test is conducted to detect underlying thyroid disorders as the thyroid hormones affect almost all metabolic activity within the body. Its level in the blood has a wide ranging influence and may be the cause of several disturbances in the body such as heart rhythm, fertility problems and menstrual disorders in women, growth and general development in children, weight gain, fatigue and so on.

Who should go for it?

  • Persons who have symptoms pointing towards hyperthyroidism such as, problem in sleeping, hand tremors, increased heart rate and nervousness, or loss in weight.
  • Persons who exhibit symptoms associated with hypothyroidism such as, gain in weight, unexplained fatigue, constipation, feeling inordinately cold, skin dryness, menstrual disturbances in women and so on.
  • A TSH test is also advised for screening newborns for hypothyroidism which can have serious consequences for the child’s normal development.
  • This test is also important for monitoring persons undergoing treatment for thyroid diseases to accurately adjust the dose.
  • People who have a lump or swelling in the neck.
  • Women who are facing infertility problems are also advised this test.
  • In some cases, it is advised to gauge pituitary gland functioning.
  • Children with delayed growth and development may be advised this test.


This is a simple blood test and there is no need for any kind of special preparation beforehand. Blood is drawn from the arm by a trained technician.

Interpretation of results

The normal range for TSH is from 0.3 to 3 mIU/L.  Earlier the normal range was considered to be between 0.5 to 5.0 mIU/L.  However, several factors are taken into consideration when interpreting the results. High levels of TSH indicate low levels of thyroid hormones in the bloodstream which may be due to an underactive thyroid. It can also be due to problems in the pituitary gland. On the other hand, low levels of TSH may indicate an overactive thyroid. Generally speaking T4 and T3 levels are also tested to give a clearer picture of thyroid function. This is because a TSH test merely indicates an abnormality in thyroid hormone levels, but the reason for this can only be found out with further testing.

Several medicines can also affect the results and should always be taken into account when interpreting results. Besides this, excessive stress or severe illness can affect hormone levels. TSH will also be low during the first three months of pregnancy.

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Written by: Nandita tripati

Date last updated: January 10, 2015

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