What Do High & Low TSH Levels Mean?

Jacqueline Slobin
Jacqueline Slobin23 Aug 2022

The thyroid gland, located at the front of your neck, produces hormones called T3 and T4 that regulate many bodily functions. Some functions that are controlled by the thyroid gland include temperature regulation, heart rate, brain development, and metabolism. Hyperthyroidism occurs when your thyroid gland is overactive and producing too much T3 and T4, while hypothyroidism occurs when your thyroid gland is underactive and not producing enough of these hormones. 

When to Get TSH Levels Checked

According to Penn Medicine, your healthcare provider may recommend that you get your TSH levels checked if you: 

  • Experienced significant weight change without changing your eating or exercise habits
  • Notice differences in the appearance of your skin, such as dryness, redness, itchiness, puffiness, or swelling near the base of your neck
  • Are always tired, experiencing muscle weakness, or joint pain
  • Are always either hot or cold
  • Are not pregnant but are missing your period
  • Are planning on getting pregnant. It is important that TSH levels are normal before pregnancy
  • Recently started thyroid therapy and your doctor wants to recheck your TSH levels

In addition, at birth baby’s TSH levels are checked to ensure proper brain development. 

What TSH Is

TSH, or thyroid-stimulating hormone, is released by the pituitary gland, which is a small endocrine gland located at the base of your brain. TSH levels measure if the thyroid gland is overactive or underactive. 

When the thyroid levels in your body are low (hypothyroidism), your pituitary gland will produce more TSH and when the thyroid levels in your body are high (hyperthyroidism), the pituitary gland will produce less TSH. Therefore, your TSH levels can show how well your thyroid gland is functioning and if there are any abnormalities. 

How TSH Is Tested

A TSH test also referred to as a thyrotropin test, is done by drawing blood from a vein in the arm. Your provider may also decide to order a T4, T3, and FT4 test depending on your symptoms and medical history. These tests measure thyroxine and other hormones produced by your thyroid. You do not need to fast or do anything to prepare if you are just getting a TSH test; however, if your provider is ordering other blood tests you may need to fast prior to the tests. 

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What High and Low TSH Levels Mean

It is important to talk through the results of all of your blood work with your healthcare provider. Your provider will be able to give you the best recommendations for a course of action if the results are abnormal. Below we outline a range of normal thyroid levels based according to UCLA Health.

Note: If you are pregnant, older in age, taking certain medications, and have a history of pituitary or thyroid conditions, your normal TSH, FT4, F4, and F3 levels may be different. An endocrinologist or other health care provider can help figure out a normal level of these hormones for you. 

  • The normal range for TSH is 0.5 to 5.0 mIU/L.
  • The normal range for FT4 is 0.7 to 1.9ng/dL.
  • The normal Total T4 level in adults is 5.0 to 12.0μg/dL.
  • The normal Total T3 level in adults is 80-220 ng/dL.

Abormal TSH Levels

According to the American Thyroid Association and UCLA Health, these are general interpretations of thyroid test results. 

Hormone levelsCondition
Low TSH, High T4Hyperthyroidism
High TSH, Low T4Primary Hypothyroidism
Low TSH, Low T4Secondary Hypothyroidism 
High TSH, Normal T4Subclinical Hypothyroidism
Low TSH, Normal T4Mild Hyperthyroidism

Thyroid Conditions Explained

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Hyperthyroidism occurs when the thyroid gland is producing too much thyroid hormone. Some of the symptoms of hyperthyroidism include but are not limited to weight loss, rapid or irregular heart rate, change in menstrual or bowel patterns, and enlarged thyroid gland. 

Some of the causes of hyperthyroidism are Grave’s disease, thyroiditis, thyroid hormone therapy, multinodular goiter, and dysfunction due to medication.

According to Johns Hopkins, Levothyroxine (Synthroid, Euthyrox, Levo-T, Levoxyl, Unithroid), Liothyronine (Cytomel), or Natural thyroid (Nature-thyroid, Westhroid) are used to treat hyperthyroidism. 


Hypothyroidism occurs when the thyroid gland does not produce sufficient amounts of hormones. Some of the symptoms of hypothyroidism include but are not limited to fatigue, weight gain, puffy face, thinning hair, impaired memory, and an enlarged thyroid gland. 

Some causes of hypothyroidism are Hashimoto’s thyroiditis, radiation, thyroid surgery, medications, and response to treatment for hyperthyroidism. Propylthiouracil (PTU) and Methimazole (Tapezole) may be prescribed to treat hypothyroidism.

This article was medically reviewed by Dr. Sonoo Advani. Dr. Advani is a Board Certified Endocrinologist as well as a Board Certified Integrative and Holistic Medicine physician and has been practicing Endocrinology since 1988. In 2002 she was Clinical Assistant Professor of Medicine with the Department of Medicine at the University of Medicine and Dentistry of NJ, Robert Wood Johnson Medical School. Dr. Advani’s philosophy for patient care is to take the best of traditional medicine and/or natural remedies as well as lifestyle changes to obtain optimal results and optimal health for her patients.


Disclaimer: The information provided by this article is not intended to replace the services of a trained health professional or to be a substitute for the medical advice of physicians. If you are experiencing an emergency, call 911 immediately or go to your nearest ER. You should contact a physician for any health issues, and particularly with respect to any symptoms that may require diagnosis or medical attention. 

Jacqueline Slobin

Jacqueline graduated from the University of Virginia in 2021 with a B.A. in Global Public Health and is a current M.D. candidate at the Icahn School of Medicine at Mount Sinai. Jacqueline has been working for Mira since April 2020 and is passionate about the intersection of public health and medical care.