That’s what your thyroid levels mean

That's what your thyroid levels mean

The thyroid plays a central role in human metabolism. It produces the hormones T3 (triiodothyronine), T4 ( thyroxine ) and calcitonin. While T3 and T4 are involved in numerous processes in energy metabolism, calcitonin plays a vital role in calcium metabolism and bone formation. If thyroid disease is suspected, a blood test is usually done to determine the various levels of the thyroid gland. We explain the meaning of the individual values ​​and the causes behind a deviation from the normal range.

Thyroid levels: diagnosis of thyroid disease

If a patient’s symptoms and history suggest that the thyroid gland is overactive or underactive, levels of the hormones T3, T4 and TSH (thyroid-stimulating hormone, thyrotropin) in the blood provide information about thyroid function. If these values ​​are within the normal range, a functional disorder of the thyroid gland can be ruled out.

If inflammation of the thyroid gland (thyroiditis) or an autoimmune disease such as Graves ‘ disease is suspected, the blood is examined for the presence of particular antibodies against components of the thyroid gland. On the other hand, the level of the hormone calcitonin in the blood is usually only measured to rule out a specific type of thyroid cancer.

Normal range of thyroid values

In the following table, we have compiled an overview of the normal ranges for your thyroid values. However, this overview only serves as an approximate orientation, as average values ​​depend on the age and sex of the patient and on the laboratory carrying out the examination.

Deviations in thyroid levels

If your thyroid values ​​deviate from the normal range, this can have various causes. A severe illness is not always behind a thyroid value that is too high or too low because blood values ​​can also be subject to daily or seasonal fluctuations. We have summarized the meaning and possible causes of increased or decreased thyroid values ​​.


Thyroid hormones: overactive or underactive?

If there is a suspicion of an underactive or overactive thyroid, a blood test usually determines the basal TSH and the free hormones T3 and T4 (fT3, fT4). Free means that the hormones in the blood are not bound to a transport substance. The following generally applies to the thyroid values ​​fT3 and fT4:

  • Values ​​too high: overactive thyroid (hyperthyroidism)
  • Values ​​too low: hypothyroidism (hypothyroidism)

In conjunction with the basal TSH value, the doctor can conclude the cause of the thyroid disease. It is essential to distinguish between a primary and a secondary dysfunction. Primary means the disorder is in the thyroid itself.

Basal TSH: indication of the cause of the dysfunction

The concentration of the thyroid hormones alone does not allow any statement to be made about the cause of the thyroid dysfunction. Therefore, the basal TSH is also determined. Basal means that the administration of TRH did not stimulate TSH production as part of a TRH test.

The resulting constellation of the thyroid values ​​fT3, fT4 and basal TSH can be interpreted by the doctor and assigned to a disease.

A deviation of the basal TSH value can have the following causes:

  • Value too high: primary hypothyroidism, secondary hyperthyroidism, medication ( MCP drops, certain active ingredients against epilepsy and mental illnesses)
  • Value too low: primary hyperthyroidism, secondary hypothyroidism, medication ( heparincortisone, opiates, medication for Parkinson’s)

Causes of primary hyperthyroidism

Primary hyperthyroidism can be caused by:

  • Morbus Basedow
  • Early stage thyroiditis
  • thyroid autonomy


Causes of primary hypothyroidism

Possible causes of  primary hypothyroidism include:

  • Iodine deficiency
  • iodine utilization disorder
  • advanced thyroid inflammation
  • surgical removal of the thyroid

Causes of secondary thyroid dysfunction

In the case of a secondary functional disorder, on the other hand, the disorder lies in a higher-level organ of the hormone control circuit, i.e. in the hypothalamus or – more frequently – in the pituitary gland.

An underactive pituitary gland most often causes secondary hypothyroidism. The pituitary gland produces too little TSH, and the thyroid gland is not sufficiently stimulated to produce T3 and T4.

On the other hand, secondary hyperthyroidism can be caused by a TSH-producing tumour in the pituitary gland – although this is relatively rare.

TRH test: safety with borderline results

If the values ​​of TSH, fT3 and fT4 are in a “grey zone”, i.e. deviate only slightly from the normal range, a TRH test can be carried out to confirm the diagnosis. After determining the basal TSH, the hypothalamic hormone TRH is injected or administered as a nasal spray to stimulate the production of TSH in the pituitary gland. After 30 minutes, another blood sample is taken, and the increase in TSH is measured.

In healthy people, the TSH should increase by two to 25 mU/l. Deviations from this range confirm the presence of pituitary or thyroid dysfunction:

  • Decreased TSH increase : primary hyperthyroidism (if fT3 and fT4 are elevated), hypopituitary gland (if fT3 and fT4 are decreased)
  • excessive TSH increase: primary hypothyroidism

However, various medications and diseases, such as Cushing’s syndrome (excessive production of the hormone cortisone), can also impact the increase in TSH. If the result of the TRH test is within the normal range, the thyroid is unlikely to be dysfunctional.


Thyroid antibodies in autoimmune diseases

To rule out an autoimmune disease as the cause of an underactive or overactive thyroid gland, the blood can be tested for particular antibodies against components of the thyroid gland:

  • Thyroid peroxidase antibodies (TPO-AK, anti-TPO): Thyroid peroxidase is an enzyme that plays a vital role in forming thyroid hormones. Antibodies against thyroid peroxidase are usually found in the blood in Hashimoto’s thyroiditis and other forms of thyroid inflammation and Graves’ disease. However, these antibodies can also be detected in five per cent of healthy people. A positive anti-TPO result alone is not proof of an autoimmune disease.
  • Thyroglobulin antibodies (TAK, TG-AK, anti-TG): Thyroglobulin is a storage protein for thyroid hormones. Antibodies against thyroglobulin can be detected in Hashimoto’s thyroiditis, other forms of thyroid inflammation, Graves’ disease, thyroid cancer and in five per cent of healthy people.
  • TSH receptor antibodies (TRAK, anti-TSH-R): The TSH receptor is the “docking point” for the hormone TSH on the thyroid gland. Antibodies against the TSH receptor are typically present in Graves’ disease. Only in a few cases can they be detected in other thyroid diseases. In healthy people, the TRAK value is negative.


The hormone calcitonin is produced in the so-called C-cells of the thyroid gland. It plays a vital role in calcium metabolism and promotes bone formation. The calcitonin level in the blood is determined if there is a suspicion of thyroid cancer (C-cell carcinoma, medullary thyroid carcinoma). Conspicuous calcitonin values ​​can have the following causes:

  • Value too high: C-cell carcinoma, kidney failure, hypergastrinemia (increased production of the hormone gastrin in the stomach), birth control pills
  • Value too low: too low a calcium level in the blood


In addition to detecting antibodies against thyroglobulin, the concentration of the protein itself in the blood can also be determined. The thyroglobulin value is increased in Graves’ disease, in benign enlargement of the thyroid gland (euthyroid goitre) and inflammation of the thyroid gland.

The thyroglobulin value is of great importance in check-ups after surgical removal of the thyroid gland due to thyroid cancer. Elevated levels of thyroglobulin after thyroidectomy can be a sign of cancer recurrence.


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