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Understanding the Thyroid: Functions, Levels, and Common Complaints
The thyroid gland is small, but it influences almost every organ. If it functions too slowly or too quickly, this is often reflected in symptoms that are initially interpreted in a completely different way.
On this page
What the thyroid gland [Schilddrüse] does in the body
Underactive thyroid (Schilddrüsenunterfunktion) [Hypothyreose]
Overactive thyroid [Schilddrüsenüberfunktion] (Hyperthyroidism)
Thyroid levels: what TSH, T3 and T4 mean
What can influence laboratory values
Thyroid nodules
When a thyroid ultrasound is recommended
Iodine and iodized salt [Jod und Jodsalz] in Austria
Take-home message
Frequently Asked Questions
What the thyroid gland [Schilddrüse] does in the body
It produces hormones that determine how fast the body works: heartbeat, body heat, digestion, and energy consumption. One can think of this as setting the body's baseline pace.
It is controlled by the pituitary gland in the brain. This sends the hormone TSH as a signal: if the body needs more thyroid hormone, TSH rises. If enough is present, it decreases again.
Underactive thyroid (Schilddrüsenunterfunktion) [Hypothyreose]
In the case of an underactive thyroid gland, the thyroid produces too little hormone. The body functions more slowly than it should. The medical term for this condition is hypothyroidism.
The symptoms usually develop over a period of months and are therefore often not noticed for a long time.
Overactive thyroid [Schilddrüsenüberfunktion] (Hyperthyroidism)
In the case of an overactive thyroid, the thyroid gland produces too much hormone. The body runs faster than it should. The medical term for this is hyperthyroidism.
Unlike with an underactive thyroid, the symptoms often start quite noticeably.
Comparison of Underactive and Overactive Thyroid (Unterfunktion and Überfunktion)
Thyroid levels: what TSH, T3 and T4 mean
TSH is usually the first parameter to be determined. It does not originate from the thyroid gland, but from the pituitary gland, and indicates how strongly it stimulates the thyroid.
T4 and T3 are the thyroid hormones themselves. They are not measured with every blood test — often only when the TSH value provides a reason to do so.
Elevated Thyroid Stimulating Hormone (TSH ↑)
May indicate an underactive thyroid [Schilddrüsenunterfunktion].
TSH ↓
This may indicate an overactive thyroid (hyperthyroidism).
The TSH value alone is not the sole deciding factor.
If the TSH level is elevated
An elevated TSH level indicates an underactive thyroid. This may seem counterintuitive at first glance, but it is not: the pituitary gland detects that there is insufficient thyroid hormone and stimulates production more intensively. The high value is the signal, not the hormone itself.
If the TSH level is decreased
Conversely, a low TSH level indicates an overactive thyroid. There is already sufficient or excess thyroid hormone present, so the pituitary gland reduces its signal.
Why a single value is rarely sufficient
Furthermore, a single value is always merely a snapshot. Whether it is of significance can only be determined in context: in relation to the symptoms, the medical history, the medication being taken, and sometimes a second measurement after a few weeks.
What can influence laboratory values
Some factors influencing a laboratory value have nothing to do with the thyroid gland, but rather with other current circumstances — such as dietary supplements or medication.
What you can contribute to this
Please bring your medication list, including dietary supplements.
Do not discontinue any medication due to a laboratory result and do not alter your dosage without prior medical consultation with a General Practitioner [Hausarzt].
Thyroid nodules
A nodule [Knoten] refers to a localized change in the thyroid tissue. Many are discovered by chance when an examination is conducted for another reason.
A nodule alone is not yet a reason for treatment.
Important
There are symptoms that require prompt medical evaluation and should not be delayed: hoarseness lasting more than two weeks, difficulty swallowing, a feeling of pressure in the neck, or swollen lymph nodes in the neck. These are not definitive signs of a serious condition — but they are reasons not to postpone an appointment.
When a thyroid ultrasound is recommended
An ultrasound of the thyroid is performed if there is a clinical indication: a palpable nodule, an enlarged thyroid, an abnormal physical examination finding, or a follow-up of known changes. Whether there is an indication in your case will be clarified during the medical consultation.
Without such an indication, an examination is not intended. Professional guidelines explicitly advise against routinely performing an ultrasound of the thyroid gland in the absence of symptoms.
The ultrasound shows the size and tissue structure. It does not provide information about the function — for that, laboratory values are required.
Overview of thyroid nodules, sonography [Sonografie], and scintigraphy [Szintigrafie]. Scintigraphy is a different diagnostic method than ultrasound.
Thyroid Ultrasound in Vienna – Book an Appointment
Iodine and iodized salt [Jod und Jodsalz] in Austria
The thyroid gland requires iodine to produce its hormones. The body cannot produce it itself — it must be ingested through the diet.
Iodized table salt
important source of iodine in Austria.
Milk and dairy products
can contribute to iodine supply; content varies
Fish and seafood
can contain large amounts of iodine; content varies
If you have a thyroid disorder, please consult your General Practitioner [Hausarzt] before taking additional iodine supplements on your own. Whether and how much additional iodine is advisable depends on the specific condition and cannot be generally stated.
Take-home message
The thyroid gland determines the basic tempo of the body. Too slow and too fast both cause complaints — just different ones.
The TSH value is a good initial indicator. However, a single value without context says very little.
Most nodules are harmless. An investigation is carried out when there is a reason for it — not on suspicion.
Frequently Asked Questions
Thyroid Ultrasound in Vienna – Book an Appointment
Sources
Show sources
- Gesundheitsportal des Bundes, „TSH — Thyreoidea-stimulierendes Hormon“, Stand 26.11.2024
- Gesundheitsportal des Bundes, „Jod — Bedarf, Quellen und Mangel“, Stand 31.10.2024
- Österreichisches Lebensmittelbuch, Codexkapitel B 21 Speisesalz, 2.2 Vollsalz, abgerufen 12.09.2026
- Arzneimittelkommission der deutschen Ärzteschaft, Drug Safety Mail 2022-52, „Verfälschte Laborergebnisse bei gleichzeitiger Anwendung von Biotin“, 22.12.2022
- S3-Leitlinie „Schilddrüsenknoten bei Erwachsenen in der hausärztlichen Versorgung“, AWMF 053-058, Version 1.0, Stand 01.12.2025, veröffentlicht am 23.03.2026, gültig bis 30.11.2030, koordinierend DEGAM
- Die Jodbroschüre der Österreichischen Schilddrüsengesellschaft, Stand 12/2024, abgerufen 12.09.2026