What are Normal Thyroid Levels?

Understanding the Normal Thyroid Levels


The thyroid gland is one of the largest endocrine glands. Shaped like a butterfly, it is located in the neck just beneath the voice box or larynx. For men, it is just below their Adam’s apple. It secretes hormones to regulate metabolism and weight by burning energy fat. Thyroid hormones are needed for a child’s growth and development and in almost every physiological process in the human body.


An imbalance in thyroid levels can wreak havoc on your overall health and well-being. It is linked to serious health conditions, such as autoimmune diseases, irritable bowel syndrome, eczema, acne, infertility, and gum disease. Understanding the normal thyroid levels is important to keep your thyroid healthy.


Endocrinologists recommend a TSH (thyroid-stimulating hormone) blood test to check problems in the thyroid gland. The range of normal thyroid levels varies from one medical laboratory to another. Every laboratory report indicates the range of normal levels they use so your doctor can evaluate the results correctly based on your health, symptoms, and other factors.


The pituitary gland produces the TSH that controls the thyroid gland function. The TSH encourages the production of (T3) triiodothyronine and T4 (thyroxine) in the thyroid. The quantity and balance of the TSH affect nearly all your physiological process, specifically your metabolism.


In the U.S., the recognized normal thyroid levels as of 2017 ranges from approximately 0.5 to 4.5 or 5.0. Endocrinologists use this normal level or reference range to identify any thyroid disorder and to arrive at the proper treatment program.


For conventional endocrinologists, the normal values are essential in measuring a person’s thyroid function. You are referred to as “euthyroid” if your TSH levels fall within these normal values.


Determining the TSH Reference Range


In determining the thyroid stimulating hormone reference range, the TSH of a large group of people in the population is measured. This is calculated in a range that is considered to represent the normal thyroid levels in a healthy population. Patients with below the normal thyroid levels are classified as having hyperthyroidism while those with higher than the normal range are deemed as having hypothyroidism.


The normal thyroid levels differ slightly depending on the age and if a person is pregnant.


  • Premature birth (28-36 weeks): 0.7 0 27 mIU/L


  • Children


  • 0 – 4 days: 1 – 39 mIU/L

  • 2 – 20 week old: 1.7 – 9.1 mIU/L

  • 21 week old – 20 years old: 0.7 – 64 mIU/L


  • Adults


  • 21 – 54 years old: 0.4 – 4.2 mIU/L

  • 55 – 87 years old: 0.5 – 8.9 mIU/L


  • During Pregnancy


  • 1st trimester: 0.3- 4.5 mIU/L

  • 2nd trimester: 0.3 – 4.6 mIU/L

  • 3rd trimester: 0.8 – 5. mIU/L


What Causes the TSH to Fluctuate?


The thyrotropin-releasing hormone (TRH) stimulates the release of TSH. The amounts of T3 and T4 in your blood largely controls your TSH levels. Your body produces more TSH to stimulate your thyroid when T3 and T4 levels are low. Alternatively, your body produces less TSH when the T3 and T4 levels are high.


Other factors that affect the TSH levels are:


  • Genetics

  • Excess or deficiency of iodine in the diet

  • Inflamed thyroid gland

  • Pregnancy

  • Exposure to radiation and other poisonous substances

  • Certain medications like cholesterol-lowering drugs, steroids, antidepressants, chemotherapy drugs

  • Thyroid cancer


If your TSH results are normal but still feel ill or unwell, talk to your doctor so he can order other laboratory or diagnostic tests.