TSH

Description of the TSH test (thyrotropin, thyroid-stimulating hormone)

TSH (thyrotropin, thyroid-stimulating hormone) is a hormone produced by the anterior lobe of the pituitary gland. This hormone is responsible for:

• regulating thyroid hormonal function,
• stimulating the production and release of thyroxine (T4) and triiodothyronine (T3),
• increasing the rate of metabolic processes occurring in the thyroid gland.

The test involves drawing blood from a vein, which is then sent to the laboratory for analysis.

What does the test diagnose?

The TSH laboratory test is one of the most commonly performed diagnostic tests used to assess thyroid function. Measuring TSH levels helps detect various thyroid disorders, including hyperthyroidism and hypothyroidism, and it is also used to monitor the effectiveness of thyroid hormone therapy. 

Elevated TSH

Elevated TSH usually indicates hypothyroidism, which in many cases may lead to Hashimoto’s disease. Sometimes a high level of thyroid-stimulating hormone also indicates a pituitary adenoma, genetic disorders, primary adrenal insufficiency, or may result from taking certain medications (e.g., antithyroid drugs).

Low TSH

Low TSH levels suggest hyperthyroidism. In some cases, it may be related to pituitary insufficiency, Graves–Basedow disease, autonomous thyroid nodules, or thyroid inflammation. Low TSH may also be caused by certain medications (e.g., dopamine, phenytoin, amiodarone).

The role of the thyroid

Despite its small size, the thyroid gland is responsible for:

• producing T4 and T3 hormones,
• regulating metabolism,
• influencing the function of the cardiovascular system.

According to data from the Central Statistical Office (GUS) from 2006, statistically every fifth person in Poland had or has a thyroid problem. Many people do not notice changes occurring in the body or simply ignore certain symptoms. 

When is it worth performing a TSH test?

A TSH test is recommended for individuals experiencing symptoms suggesting thyroid dysfunction. The most common symptoms of hypothyroidism include:

• fatigue, drowsiness, weakness, and apathy;
• weight gain despite no dietary changes;
• cold sweats, feeling cold, and sensitivity to low temperatures;
• frequent constipation;
• dry skin;
• hair loss;
• swelling, especially around the face;
• depression and emotional disturbances; 
• concentration problems;
• irregular periods;
• reduced libido.

In hyperthyroidism, symptoms may include:

• weight loss, even with increased appetite;
• feeling hot;
• increased sweating;
• irritability, nervousness, anxiety, restlessness;
• insomnia;
• difficulty concentrating;
• tremors of the hands, tongue, or eyeballs;
• more frequent bowel movements, even diarrhea;
• rapid heartbeat, palpitations;
• shortness of breath;
• muscle weakness;
• hair loss;
• typical symptoms of Graves–Basedow disease: bulging eyes, double vision, swelling and redness of the eyelids or conjunctiva;
• in women – menstrual irregularities (infrequent periods or absence of menstruation);
• in men – decreased libido and sometimes erectile dysfunction.

Measuring TSH levels during pregnancy

Thyroid hormones are essential for proper fetal development. Their correct levels ensure healthy development of the brain, skeletal system, and nervous system. The test is ordered for individuals with suspected hyperthyroidism or hypothyroidism. During pregnancy, estrogen and human chorionic gonadotropin (hCG) may influence the increase or decrease of TSH production. Depending on the trimester, the reference range for TSH may differ from the standard range.

How often should TSH be tested during pregnancy?

If TSH levels are abnormal, further management—including the frequency of follow-up tests—should be determined by an endocrinologist. In pregnant women with hyperthyroidism, the risk of miscarriage or preterm birth may increase.

Learn more:

• Thyroid tests
• Hypothyroidism – causes, symptoms and treatment
• Hyperthyroidism – symptoms, causes and treatment
• Hashimoto’s disease – symptoms, diagnosis and treatment
• Chronic fatigue and lack of energy — causes, symptoms and treatment

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How to prepare for a TSH blood test?

No special preparation is required for the test. It is not recommended to follow any special diet. If you feel unwell after the blood draw, inform your doctor or nurse. During the test, a small amount of blood is taken, which should not significantly affect the patient's well-being.

Should the TSH test be done on an empty stomach?

It is recommended that the patient be fasting (due to the circadian rhythm). In this case, you should avoid eating for 8–12 hours before the blood draw and come for the test in the morning. There is no need to discontinue any medications before the TSH test.

TSH test and medications

Before the blood draw, inform the healthcare professional about any medications, herbs, or dietary supplements you are taking, as these may affect the test result. Do not take over-the-counter medications such as painkillers before the test. If you take regular medication, the decision about testing before taking your morning dose should be discussed with your doctor. 

What is the normal TSH level in the blood?

The normal concentration of thyroid-stimulating hormone (TSH) in the blood ranges from 0.2–0.4 to 4.0–4.25 mIU/L for an adult. If the result is below the normal range, it indicates hyperthyroidism. Conversely, if the result exceeds the upper limit, it may be a sign of hypothyroidism.

However, it should be noted that these reference ranges are not fixed. Depending on the facility where the test is performed, TSH and other laboratory values may differ slightly. This variation is influenced by the reagents and equipment used by laboratory technicians. In the case of abnormal results, it is recommended to consult a doctor for a detailed discussion. The doctor may decide to order further diagnostic tests, such as: 

• FT3 and FT4 level testing,
• thyroid ultrasound,
• complete blood count,
• testing for anti-thyroid antibodies.

Factors that may affect the test result

• use of thyroid medications,,
• pregnancy,
• stress.

Which specialists should you consult in case of abnormal results?

• Endocrinologist
• Internist 

TSH test results

Check HERE