What is TSH ?

TSH stands for thyroid stimulating hormone. It is produced and released into the bloodstream by the pituitary gland (a pea-sized structure), which is located at the base of your brain. It is responsible for regulating many hormones released by the thyroid gland.

Furthermore, your thyroid gland controls different bodily functions, including metabolic rate, heart and digestive functions, muscle control, brain development, by releasing a steady amount of thyroid hormones.

Thyroid gland produces two major thyroid hormones:

In addition to the above, the production and release of thyroid hormones are controlled and regulated by thyroid stimulating hormone (TSH), which is secreted by the pituitary gland.

How TSH Levels Change ?

When levels of thyroid hormones decrease below normal, the pituitary gland releases the Thyroid stimulating hormone. This hormone binds to the receptor on the thyroid cells. This causes thyroid cells to produce more hormones (T3 and T4) and release them into the bloodstream. Once the levels of thyroid hormones rise, the pituitary gland then decreases TSH production.

In this way, the two glands work together to make sure the right amount of thyroid hormones are produced.

  1. First, your pituitary gland senses the level of thyroid hormone that is released into the bloodstream by your thyroid gland.

  2. When your thyroid gland, due to illness, stress, surgery, obstruction, or due to whatever reason, doesn’t produce enough thyroid hormone, your pituitary gland detects the reduced levels of thyroid hormones and moves into action by making more TSH, which then triggers your thyroid to make more thyroid hormones (T3 and T4).

    This is the pituitary’s effort to raise the levels of thyroid hormone and return the system to normal.

  3. If your thyroid is overactive and producing too much thyroid hormone, due to disease or taking too high a dose of thyroid hormone replacement drugs, your pituitary gland senses that there is too much of the hormone circulating and slows or shuts down TSH production.

    This drop in TSH is an attempt to return circulating thyroid hormones levels to normal.

Why do I need a TSH test?

A TSH test can be used to check how well your thyroid gland is functioning. It measures the amount of thyroid stimulating hormone that your pituitary gland is secreting. Your doctor may order a TSH test, if you’re experiencing symptoms of a thyroid disorder.

TSH Test

Thyroid diseases can be categorized as either hypothyroidism (too little thyroid hormone) or hyperthyroidism (too much thyroid hormone)

Symptoms of hypothyroidism, also known as underactive thyroid, include:

  • Hair Loss
  • Puffy Face
  • Dry Skin
  • Slow Heartbeat
  • Constipation
  • Irregular Periods in women
  • Loss of interest in sex
  • Cold Sensitivity
  • Tiredness
  • Sore Muscles
  • Joint Pain
  • Depression
  • Weight Gain
Symptoms of Hypothyroidism

Symptoms of hyperthyroidism, also known as overactive thyroid, include:

  • Bulging Eyes
  • Abnormal Heart Rate
  • Diarrhea
  • Weight Loss
  • Irritability
  • Itching
  • Heat Intolerance
  • Stress
  • Sleeplessness
  • Vision Problem
  • Frequent Sweating
  • Irregular Mensuration
  • Nervousness
Symptoms of Hyperthyroidism

TSH tests are also used to screen newborn babies for underactive thyroid, and to diagnose fertility problems in women.

This test is frequently ordered along with or prior to a free T4 test. Other thyroid tests that may be ordered include total or free T3 tests. TSH, free T4 and sometimes free T3 may be ordered together as a thyroid panel.

What does the TSH test result means ?

High TSH levels can mean your thyroid is not making enough thyroid hormones, a condition called hypothyroidism. Low TSH levels can mean your thyroid is making too much of the hormones, a condition called hyperthyroidism.

Please note, a TSH test does not explain why TSH levels are too high or too low. If your test results are abnormal, your health care provider will probably order additional tests to determine the cause of your thyroid problem. These tests may include:

  • T4 thyroid hormone tests
  • T3 thyroid hormone tests
  • Tests to diagnose Graves’ disease, an autoimmune disease that causes hyperthyroidism
  • Tests to diagnose Hashimoto’s thyroiditis, an autoimmune disease that causes hypothyroidism

How do I get ready for TSH test?

It’s important to tell your doctor about all of the medications you’re currently taking. Many multivitamins, supplements, and prescription medications may interfere with the accuracy of the TSH test results. Therefore, their use should be discussed with your doctor, prior to testing.

You may need to avoid using these drugs before the test. However, don’t stop taking your medications unless your doctor tells you to do so.

In addition to the above, you may also need to fast (not eat or drink) for several hours before the test. Remember, TSH levels can vary throughout the day, so it’s best to have this test done early in the morning. Your health care provider will let you know if there are any special instructions to follow.

How is TSH Test Performed?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial (a small glass or plastic bottle). You may feel a little sting when the needle goes in or out.

Blood sample from a vein
Blood sample from a vein

The entire procedure should only take a few minutes to complete. The blood sample will be sent to a lab for analysis. Once your doctor receives the test results, they’ll schedule an appointment with you to discuss the results and explain what they may mean.

TSH Test Reference range

TSH Test reference range are only one indicator of how your thyroid is functioning. They vary by gender, age, and other factors. In general, normal, low, and high TSH levels are:

AgeReference Range
( μIU/mL)
( μIU/mL)
( μIU/mL)
0-5 Days0.70 – 15.20<0.70>15.20
6 Days – 2 Months0.70 – 11.00<0.70>11.00
3 Days – 11 Months0.70 – 8.40<0.70>8.40
1 – 5 Years0.70 – 7.00<0.70>7.00
6 – 10 Years0.60 – 4.80<0.60>4.80
11 – 15 Years0.50 – 4.70<0.50>4.70
> 20 Years (Adults) 0.27 – 4.70<0.27>4.70

Dear reader, I have also attached my Thyroid Function Test Report for your reference. (Click Here to see report)

TSH levels in women

Women are at greater risk for developing abnormal TSH levels during menstruation, when giving birth, and after going through menopause.

Furthermore, a 2017 study showed that older women are especially at risk for developing thyroid cancer if they have high TSH levels along with thyroid nodules.

TSH levels in men

Both high and low TSH can affect fertility. Men with hypothyroidism or hyperthyroidism both had fewer normally shaped sperm.

In addition, men are more susceptible than women to complications like irregular development of the genitals if they have high TSH. Taking thyroid hormone replacement therapy may be necessary for men to balance TSH.

TSH levels in children

TSH levels in children can vary based on their age. A 2008 study that closely measured TSH levels in kids from birth to as old as 18 years found wildly different TSH levels throughout their lives.

And though TSH tends to be high for the first month after they’re born, a child’s TSH levels will gradually decrease as they get closer to adulthood before rising again as they age.

TSH levels in pregnancy

Pregnancy hormones naturally increase the levels of certain thyroid hormones in the blood. This is essential for the development of the fetal brain and nervous system.


At the same time, the levels of TSH in the blood decrease. As a result, doctors use lower reference ranges for pregnant women.

Levels of TSH in the blood increase gradually during the second and third trimesters, but they remain lower than normal levels in women who are not pregnant.

Doctors carefully monitor TSH levels throughout pregnancy. Having unusually high or low levels can affect the risk of miscarriage and cause pregnancy-related complications, such as:

  • preeclampsia
  • premature birth
  • low birth weight
  • congestive heart failure

When TSH Test alone is Not Enough ?

During diagnosis, most doctors use the thyroid stimulating hormone test to evaluate thyroid function and determine the optimal course of treatment. There are times, however, when a TSH may be insufficient.

For example, free T4 test in addition to TSH is usually ordered, if a doctor suspects thyroid dysfunction arising from disease of the pituitary gland or hypothalamus. Likewise, if the TSH is normal, but a person still has symptoms of being hyperthyroid or hypothyroid, free T4 test may be ordered.

TSH is also not necessarily sufficient to monitor hypothyroidism during pregnancy, therefore, a T4 and free T4 tests are often recommended. Depending on the clinical situation, other thyroid tests that may be ordered include triiodothyronine (T3), free T3 and thyroid antibody tests.


Doctors can use the TSH test results to diagnose thyroid conditions, such as hypothyroidism and hyperthyroidism.

Normal TSH reference range can vary widely, depending on a person’s age, gender, and other factors. A reference range can also vary between different laboratories, however, for most adults (>20 Years), the normal range falls between 0.27 and 4.70 μIU/mL.

Furthermore, make sure you get your TSH levels tested regularly, especially if you have a family history of thyroid disorders or have seen abnormal TSH levels on previous test results.

Follow all the instructions your doctor gives you to stop taking certain medications or eating certain foods before a TSH test to make sure the results are accurate. This way, your doctor can give you a treatment plan that’s best for the cause of abnormal TSH.

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