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Understanding thyroid levels - what your blood count tells you

The thyroid is an endocrine gland located in the neck area of the human body that produces hormones regulating metabolism and various other bodily functions.

These hormones, especially thyroxine (T4) and triiodothyronine (T3), influence energy consumption, body temperature, growth and development, the cardiovascular system, and emotional health.

Abnormal levels can indicate disorders such as hyperthyroidism or hypothyroidism, which can have significant effects on health. Therefore, it's worth taking a look at thyroid levels from time to time.

What is the thyroid, anyway?

The thyroid is a butterfly-shaped endocrine gland situated in the neck area, producing crucial hormones that regulate metabolism and numerous bodily functions.

Eine virtuelle Abbildung der Schilddrüse

The term "endocrine" refers to the body's endocrine system, which consists of various glands producing hormones released into the bloodstream to regulate and coordinate various bodily functions. One of these glands is the thyroid.

What does the thyroid regulate exactly?

The primary function of the thyroid is to produce and release thyroid hormones that regulate a broad range of bodily functions. Here are some key tasks of the thyroid:

  • Metabolism Regulation: Thyroid hormones, especially thyroxine (T4) and triiodothyronine (T3), influence metabolism throughout the body.
  • Body Temperature Control: Thyroid hormones contribute to regulating body temperature by increasing energy consumption and heat production.
  • Growth and Development: Thyroid hormones are crucial for the growth and development of organs and tissues, including the brain and skeletal system, especially during childhood and adolescence.
  • Cardiovascular System Regulation: Thyroid hormones influence heart rate and blood pressure. An overproduction of these hormones can lead to an accelerated heartbeat (tachycardia).
  • Emotional Health: Thyroid hormones impact mood and mental well-being. Hyperthyroidism can cause nervousness and anxiety, while hypothyroidism can lead to depressive symptoms.
  • Menstrual Cycle Regulation: The thyroid affects the menstrual cycle and fertility in women. Maintaining Healthy Body Weight: Thyroid hormones play a role in regulating body weight by influencing energy consumption.

Thyroid Values Under the Microscope

The thyroid plays a crucial role in maintaining hormonal balance in the body. Thyroid values, obtained from a blood test, are key to assessing thyroid health and, consequently, overall well-being.

The most important thyroid values measured in a blood test include thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3).

It's essential to understand that thyroid values should not be considered in isolation. They should always be evaluated in conjunction with individual symptoms and the patient's clinical history. A doctor will also consider other potential causes for deviations in thyroid values, such as medications or other health issues.

Regulation of Thyroid Function: Thyroid-Stimulating Hormone (TSH)

Thyroid-stimulating hormone (TSH), also known as thyrotropin, is produced in the pituitary gland and plays a crucial role in regulating thyroid function. TSH's main function is to control the thyroid's activity.

  • Stimulation of the Thyroid: TSH binds to receptors on thyroid cells, stimulating them to produce and release thyroid hormones.
  • Metabolism Regulation: Thyroid hormones released by the thyroid influence metabolism throughout the body.
  • Energy Balance Control: TSH and the hormones released by the thyroid contribute to regulating the body's energy balance, influencing nutrient utilization, fat metabolism, and heat production.
  • Impact on Growth and Development: Thyroid hormones are essential for the normal growth and development of organs and tissues, especially during childhood and adolescence.
  • Hormone Level Regulation: When thyroid hormone levels in the blood rise, TSH production is reduced to prevent overproduction of thyroid hormones, and vice versa.

Thyroid Hormones: Thyroxine (T4) and Triiodothyronine (T3)

Free thyroxine (fT4) and free triiodothyronine (fT3) are the biologically active forms of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones play a crucial role in regulating various functions in the body.

  • Metabolism Regulation: fT4 and fT3 are the main regulators of metabolism in the body, influencing energy consumption, nutrient utilization, and fat metabolism. Maintaining an appropriate level of fT4 and fT3 is crucial to ensuring the body produces and efficiently uses enough energy.

  • Temperature Regulation: Thyroid hormones, especially fT3, contribute to regulating body temperature by influencing heat balance, increasing body temperature to maintain normal levels.

  • Impact on the Cardiovascular System: fT4 and fT3 affect the cardiovascular system by increasing heart rate and enhancing the contractility of the heart muscle. This results in an increased pumping capacity of the heart and influences overall body circulation.

  • Growth and Development: During growth and development, especially in childhood and youth, fT4 and fT3 are crucial for the normal development of organs and tissues. A deficiency of thyroid hormones during this phase can lead to growth disorders.

  • Brain Function: Thyroid hormones, including fT4 and fT3, influence brain function, maintaining normal mental function, mood, and overall well-being. Energy Balance Regulation: fT4 and fT3 influence the body's energy balance by affecting nutrient utilization and the production of ATP (adenosine triphosphate), the cells' energy source.

These Are the Healthy Thyroid Values for Adults

Note: Thyroid values can vary from one laboratory to another. Deviations from these values may indicate thyroid disorders, but an accurate diagnosis should always be made by a doctor. The hormones thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) are considered:

Thyroidparameters Normal reference range

Thyrotropin (TSH)

0.4  - 4.0 milli-international units per liter (mIU/L)
Free thyroxine (fT4) 0.9 - 1.7 nanograms per deciliter (ng/dL)
Free triiodothyronine (fT3) 2.3 - 4.2 picograms per milliliter (pg/mL)


Thyrotropin (TSH)
The normal TSH value is usually between 0.4 and 4.0 milli-international units per liter (mIU/L). A TSH value within this range indicates that the thyroid gland is producing hormones at an appropriate level and that the metabolism is functioning normally.Free Thyroxine (fT4).

Free thyroxine (fT4)
The normal range for free thyroxine is usually between 0.9 and 1.7 ng/dL (Nanograms per deciliter). A balanced fT4 level is crucial for maintaining energy levels and metabolic processes in the body.

Free Triiodothyronine (fT3)

The normal range for free triiodothyronine is typically between 2.3 and 4.2 pg/mL (Picograms per milliliter). A healthy fT3 level supports physical and mental vitality.

The following table indicates at what point suspicion arises for either an underactive or overactive thyroid:

 Parameters  Hypothyroidism Hyperthyroidism
TSH (mIU/L)  > 4.0  < 0.4
fT3 (ng/dL)  < 80  > 180
fT4 (µg/dL)  < 4.5 > 12.0


What do elevated or reduced thyroid values indicate?

Normal thyroid values logically indicate a healthy thyroid function and a smoothly regulated system in the body. Deviations occur when the thyroid either produces too many or too few thyroid hormones, indicating either hyperthyroidism or hypothyroidism. However, the TSH value can also be a crucial factor.

Depending on the present thyroid values, different typical constellations and possible conditions emerge:

Reduced TSH, Reduced T3 and T4

This may indicate a rare deficiency of the pituitary gland (anterior pituitary insufficiency), where the pituitary gland does not appropriately respond to low T3 and T4 levels.

Normal/Elevated TSH, Elevated T3 and T4

Overactivity of the pituitary gland can lead to normal or elevated TSH levels, while T3 and T4 are elevated. However, this is rare.

Elevated TSH, Reduced T3 and T4

This suggests hypothyroidism. The thyroid does not produce enough hormones, prompting the pituitary gland to compensate with increased TSH secretion. Autoimmune conditions like Hashimoto's thyroiditis are common causes.

○ Reduced TSH, Elevated T3 and T4

This indicates hyperthyroidism. Thyroid hormones T3 and T4 are excessively present in this case. Causes may include Graves' disease, thyroid inflammation, or autonomously hormone-producing thyroid nodules.

○ Elevated/Reduced TSH, Normal T3 and T4

In the early stages of thyroid disorders, thyroid values may still be within the normal range, but TSH levels can already be elevated or reduced.


 status TSH T3 & T4
Hypothyroidism (rare)  decreased  decreased
increased  decreased
Hyperthyroidism (rare) 
normal / elevated elevated
Hyperthyroidism  decreased increased

Overall, thyroid levels are an important indicator of thyroid function and can provide doctors with valuable information to make the correct diagnosis and initiate appropriate treatment. It is advisable to have regular health checks to ensure that thyroid levels are within the normal range and that any problems can be detected and treated early.