Thyroid-stimulating hormone: normal and abnormalities

Thyroid-Stimulating Hormone (TSH) — a Key Regulator of Thyroid Function. IT is a key regulator of thyroid gland function. It is responsible for maintaining stable levels of thyroxine (T4) and triiodothyronine (T3), which affect metabolism, energy balance, heart rhythm, and the reproductive system. When hormone levels are within the normal range, the body functions harmoniously; deviations may cause changes in well-being and require correction.

What Is TSH and How Does It Affect the Thyroid Gland?

As noted above, TSH is the main regulator of thyroid gland function.

When TSH levels are above normal, it enters the bloodstream in excessive amounts, which can lead to hyperthyroidism.

Its symptoms include:

• anxiety;
• tachycardia;
• marked irritability;
• noticeable weight loss;
• general weakness;
• increased fatigue;
• insomnia;
• visual impairment;
• eyelid swelling;
• diarrhea.

When TSH is decreased, it leads to hypothyroidism. Its key symptoms include:

• menstrual irregularities;
• unexplained swelling;
• pronounced bradycardia;
• noticeable skin dryness;
• significant weakness.

Hair loss and memory impairment may also occur.

Preparation for a TSH Test

The test is recommended to be performed fasting before 6 a.m. It has been proven that hormone concentration is highest between 2 and 6 a.m. Physical and emotional stress should be avoided before testing.

What Functions Does TSH Perform in the Body?

By acting on specific receptors in the thyroid gland, TSH stimulates the activation and production of thyroxine.

An increase in cAMP levels mediates the effect of TSH on the biosynthesis of T3 (triiodothyronine) and T4 (thyroxine). These growth hormones are critically important for humans. TSH also has long-term effects, such as increasing protein, nucleic acid, and phospholipid synthesis, as well as altering the size and number of thyroid cells.

How to Properly Take a Blood Test for TSH

The test material is blood serum obtained from a vein. For the most accurate result:

• avoid physical and emotional stress, smoking, alcohol, fatty and spicy foods for 2–3 days;
• fasting period should be 9–10 hours;
• women should take the test 5 days before menstruation or 5 days after it ends;
• avoid smoking for at least 60 minutes before the test.

Patients taking thyroid medications should skip the morning dose on the day of testing.

Normal TSH Levels by Age and Sex

• women: 0.3–4.2 µIU/mL;
• pregnant women: 0.2–3.5 µIU/mL;
• men: 0.4–4.0;
• newborns: 1.1–17.0;
• infants up to 2.5 months: 0.6–10.0;
• up to 14 months: 0.4–7.0;
• children up to 5 years: 0.4–6.0;
• adolescents up to 14 years: 0.4–5.0;
• over 14 years: 0.4–4.0.

TSH Levels in Women: Important Age-Related Features

In women, TSH levels change throughout life. During reproductive years, they usually range from 0.3 to 4.2 µIU/mL; during pregnancy, they tend to be lower (0.2–3.5 µIU/mL). During menopause, TSH levels often gradually increase, requiring regular monitoring and endocrinologist consultation.

Free Thyroxine: Normal Levels in Women

In addition to TSH, endocrinologists often order a free thyroxine (T4) test. This indicator reflects how actively the thyroid gland is functioning. Normal free T4 levels in women are approximately 0.8–1.8 ng/dL (depending on the laboratory) and should be evaluated together with TSH. Combined interpretation allows for more accurate diagnosis and treatment selection.

So, TSH reference ranges depend on sex and age. The indicator can change sharply during adolescence due to hormonal changes in the body. The test results will show the level of antibodies to TSH and will also indicate high-sensitivity, biotin-independent TSH. This makes it possible to draw conclusions about thyroid dysfunction (online consultation — find out your TSH reference range).

High TSH: Symptoms and Possible Causes

Elevated TSH may indicate hypothyroidism, iodine deficiency, autoimmune thyroid disease, or pituitary dysfunction. It is often associated with low T4 and T3 levels.

Symptoms of high TSH:

1. Constant fatigue and weakness.

2. Tendency to gain weight.

3. Sensitivity to cold, low body temperature.

4. Drowsiness, slowed thinking.

5. Swelling of the face and limbs.

6. Dry skin, brittle hair and nails.

7. Menstrual irregularities.

What to Do If TSH Is Elevated

Do not start treatment on your own. The physician evaluates free T4, T3, and, if necessary, thyroid peroxidase antibodies. Treatment depends on the combination of test results and is determined by an endocrinologist.

Causes of Elevated TSH

• primary hypothyroidism;
• iodine deficiency;
• thyroid diseases;
• adrenal insufficiency;
• preeclampsia;
• pituitary tumors;
• history of thyroidectomy;
• autoimmune thyroiditis (Hashimoto’s);
• TSH-secreting tumors;
• reduced sensitivity to T4 and T3;
• certain psychiatric disorders;
• lead poisoning;
• recovery phase after severe somatic illnesses.

Symptoms of Low TSH

• persistent feeling of cold;
• fatigue, excessive sleepiness;
• depression;
• memory problems;
• weight gain;
• constipation;
• low blood pressure, slow heart rate;
• pale, dry, flaky skin and dry hair;
• menstrual disorders, infertility.

Laboratory tests may reveal anemia and high cholesterol. Severity varies from mild to severe, with possible complications including heart disease and coma.

Causes of Decreased TSH

• thyroid disorders;
• autoimmune thyroiditis;
• Plummer’s disease or toxic adenomas;
• hypothalamic or pituitary dysfunction;
• stroke or head trauma;
• infections, hypocorticism;
• cachexia and certain medications;
• intense physical activity, stress, prolonged fasting, strict diets.

How to Increase TSH Levels If They Are Low

Hypothyroidism is treated with hormone replacement therapy, such as levothyroxine. In some cases, the condition may resolve spontaneously, but most patients require lifelong monitoring and treatment.

Frequently Asked Questions

What does elevated TSH mean?
It usually indicates hypothyroidism, iodine deficiency, or autoimmune thyroid disease.

What should be done if TSH is elevated?
Repeat the test, check free T4/T3, and consult an endocrinologist.

What is the normal TSH level for women?
Approximately 0.3–4.2 µIU/mL; during pregnancy, reference ranges differ.

When should TSH and free thyroxine be tested?
In cases of fatigue, weight changes, hair loss, menstrual irregularities, insomnia, irritability, or lethargy.

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