TSH

TSH (thyrotropin, thyroid-stimulating hormone) is secreted by the pituitary and “tells” the thyroid how much hormone to produce. Blood TSH is the first and most sensitive test when checking whether the thyroid is underactive or overactive, and is also used to monitor thyroid treatment.

Who the test is for

• people who are tired, sensitive to cold, gaining weight or have dry skin and constipation, which may indicate an underactive thyroid;
• people with restlessness and palpitations, weight loss, sweating or trembling hands, which may indicate an overactive thyroid;
• people with an enlarged thyroid or a thyroid nodule;
• women with irregular periods or infertility, women planning pregnancy and pregnant women, particularly those at increased risk;
• people with high cholesterol, atrial fibrillation or another autoimmune disease, such as type 1 diabetes;
• people taking medicines that can affect the thyroid, such as amiodarone or lithium;
• people treated with levothyroxine or medicines reducing thyroid activity, to monitor treatment.

What TSH is and what it shows

The pituitary, a small gland at the base of the brain, monitors blood thyroid hormones, thyroxine (T4) and triiodothyronine (T3). When levels are too low it secretes more TSH, stimulating the thyroid to work harder. When levels are too high, TSH secretion decreases.

Because of this feedback, TSH changes even in mild disorders, often before thyroid hormones leave the reference range. It is therefore usually measured first, alongside free thyroxine (fT4), showing how much hormone the thyroid actually produces. TSH alone does not reveal the cause: that requires antibodies anti-TPO and anti-TG, ultrasound and other tests selected by a doctor.

Who benefits from checking and when is described in the article on early detection of thyroid dysfunction.

Save with a panel

Test TSH is also included in these panels.

Thyroid health panelTSH, T3, T4Price of individual tests: 30.00€27.00€Details ›Thyroid panel with free hormone fractionsTSH, fT3, fT4Price of individual tests: 30.00€27.00€Details ›Complete thyroid panelTSH, T3, T4, fT3, fT4 and 2Price of individual tests: 102.00€92.00€Details ›

All panels including TSH (23) ›

Preparation and sample

TSH is measured in venous blood. Fasting is unnecessary for thyroid tests, but if tests requiring it, such as glucose or blood lipids, are performed simultaneously, come fasting. Morning collection is best and, for monitoring, preferably at a similar time each day because TSH varies slightly during the day.

• If you take levothyroxine, take the tablet after blood collection on the testing day unless your doctor says otherwise. Do not stop treatment yourself.
• If you take biotin (for example hair and nail supplements), mention this during collection. With some methods, high biotin doses falsely lower TSH and raise fT4, making results resemble an overactive thyroid.

How to interpret the result

The reference range depends on method and partly age and is printed on your report. Different, lower limits apply in pregnancy. A doctor interprets results alongside fT4, symptoms and medicines.

Raised TSH

Raised TSH means the pituitary is stimulating a thyroid working less effectively. If fT4 is also low, this indicates an underactive thyroid (hypothyroidism), most commonly caused by Hashimoto’s thyroiditis. Raised TSH with normal fT4 is called subclinical hypothyroidism. A doctor usually repeats testing after several weeks to three months because TSH can return to normal, for example after an illness. In people already taking levothyroxine, raised TSH most often means the dose is too low or the medicine is not taken regularly.

Low TSH

Low TSH with raised fT4 or fT3 indicates an overactive thyroid (hyperthyroidism), most often due to Graves’ disease, autonomously hormone-producing nodules or thyroid inflammation. In people taking levothyroxine, low TSH can mean the dose is too high. TSH is physiologically lower in the first trimester of pregnancy and can also be temporarily lowered by severe illness and some medicines, such as corticosteroids.

Less often, the cause is within the pituitary itself. Then fT4 is low while TSH is low or unexpectedly normal, and a doctor refers for further investigation.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list. Because TSH is most often interpreted alongside thyroid hormones, a more practical option is the Thyroid panel with free hormone fractions, containing TSH, fT3 and fT4.

Frequently asked questions

Can I drink coffee before blood collection for thyroid tests?

Fasting is not required for TSH and thyroid hormones, so a cup of coffee is not an obstacle. If glucose, lipids or other fasting tests are performed simultaneously, have coffee after collection.

Should I take my thyroid tablet before blood collection?

On the collection day, levothyroxine is usually taken afterwards so that results, particularly fT4, are comparable with earlier ones. Do not stop treatment for days before testing unless your doctor explicitly tells you to.

Is TSH enough to check the thyroid?

Often as a first step: normal TSH means normal thyroid function in most people. With pronounced symptoms, pregnancy, pituitary disease and treatment monitoring, a doctor requests fT4 alongside TSH, and fT3 and antibodies if necessary.

How often should TSH be checked while taking treatment?

After starting treatment or changing the dose, TSH is checked only after several weeks because it needs time to stabilise. Once the dose is stable, checks are less frequent, most often annually, as agreed with a doctor.