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Thyroid Stimulating Hormone Test: Why and How is it Done?

Medically reviewed by Mary Rani Cadiz, MD · Obstetrics and Gynecology

Written by Nikita Bhalla · Updated Jun 24, 2022

    Thyroid Stimulating Hormone Test: Why and How is it Done?

    The thyroid-stimulating hormone test (TSH test) helps measure the amount of thyroid-stimulating hormone in the blood. The pituitary gland located at the base of the brain produces TSH. This pituitary gland is responsible for the number of hormones released by the thyroid.

    The thyroid is a butterfly-shaped, small gland situated in the front of the neck. Doctors believe it is an important gland as it produces three primary hormones like:

    • Calcitonin
    • Triiodothyronine (T3)
    • Thyroxine (T4)

    The thyroid controls several different body functions that include growth and metabolism with the help of these three hormones.

    An excess of TSH may signal that the thyroid hormones are not producing enough such as seen in cases of hypothyroidism. Meanwhile, low TSH may mean an excess of thyroid hormones. Studies find that the pituitary gland and thyroid work together to produce the right amount of TSH. However, when the teamwork is disturbed or their functions are affected, the thyroid produces either excess or too low thyroid hormones.

    In women, TSH levels may decrease a bit during menstruation, pregnancy, or menopause but fluctuations may be normal.

    Typically, a TSH test is performed to  check if there is any abnormal thyroid hormone production. Also, the test helps to detect whether the thyroid gland is overactive or underactive. By measuring TSH levels, a doctor understands how well the thyroid is functioning.

    tsh test

    Why is a TSH test done?

    A doctor may suggest a thyroid stimulating hormone test if a person is experiencing the symptoms of a thyroid disorder, which can be either hyperthyroidism or hypothyroidism.


    It is a condition where the thyroid gland produces excess hormones, boosting the body’s metabolism.

    The symptoms of hyperthyroidism include insomnia, increased appetite, tremors, increased heart rate, puffiness, bulging eyes, anxiety, and difficulty in sleeping.

    The following is the list of common causes of hyperthyroidism:

    • Thyroid nodules are benign lumps that sometimes form on the thyroid. When these lumps become overactive as they begin to increase in size, making the thyroid produce excess hormones. 
    • Graves’s disease is a common disease where the thyroid becomes larger and produces excess hormones. 
    • Excess iodine in the body can cause the thyroid to release excess hormones. This condition can also occur when a person uses excess iodine medicines. These drugs include Amiodarone that helps treat heart arrhythmias as well as cough syrups.
    • Thyroiditis too can trigger hyperthyroidism. This may occur when the swelling causes the thyroid to produce excess hormones and release them at once.


    Hypothyroidism is a disorder where the thyroid gland produces too little thyroid hormone, slowing down the body’s metabolism. The common hypothyroidism symptoms include lower concentration levels, fatigue, constipation, poor tolerance to cold, hair fall, and irregular menstrual period.  

    The following are some of the common causes of hypothyroidism.

    • The body uses iodine to produce thyroid stimulating hormones. However, when the body lacks iodine, it can lead to hypothyroidism. 
    • Hashimoto’s disease is an autoimmune health disorder where the body attacks its own thyroid cells. This condition may not show any symptoms, hence, if the doctor suspects it, a TSH blood test may be advised.
    • Thyroiditis that is caused due to inflammation of the thyroid gland may be confirmed using the TSH test.

    Prerequisites of a TSH test

    There is no specific preparation needed for a standard thyroid-stimulating hormone test. Fasting is not necessary. However, your doctor may also ask to avoid the use of some medicines before the test as those drugs may affect the results.

    TSH test: Understanding the results

    The normal TSH levels are 0.4 to 4.0 milli-international units per liter. If a person is being treated for a thyroid abnormality, the normal range is 0.5 to 3.0 milli-international units per liter. 

    If a person has a TSH value above a healthy range, it indicates his or her thyroid is underactive. This may indicate that he or she is suffering from hypothyroidism. When the thyroid gland is underactive, it produces fewer hormones, hence, the pituitary gland releases excess TSH to stimulate it.

    If an individual has a TSH value below the normal range, it may indicate his or her thyroid is overactive, which usually occurs in hyperthyroidism. When the thyroid produces excess thyroid hormones, the pituitary glands release less thyroid stimulating hormones.

    Depending on the thyroid stimulating hormone test results, a doctor can suggest medication, treatments, and other medical tests.

    When should a TSH test be repeated?

    To confirm the thyroid gland disorder you may be asked to repeat the test. If you are undergoing treatment, your doctor may ask you to repeat the TSH blood test after a few months to check for the effectiveness of treatment. For newly diagnosed conditions or for severe conditions, the doctor may advise repeating the test at regular intervals to monitor disease progression and treatment.

    TSH test Procedure

    A thyroid stimulating hormone test is similar to other blood tests. Typically, a healthcare expert takes a sample of blood from a vein on the inside of the elbow.

    The expert will first clean the skin of the selected area and tie an elastic band around the upper arm to draw blood easily. He or she will insert the needle and draw blood from a vein filled with blood.

    Once the expert draws enough blood, he or she removes the needle and elastic band, cleans the area, and applies a bandage.

    The expert, then, labels the blood sample and sends it to the laboratory for testing.


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Mary Rani Cadiz, MD

    Obstetrics and Gynecology

    Written by Nikita Bhalla · Updated Jun 24, 2022

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