TSH Reference Ranges: Reference Values and What Abnormalities Mean

Thyroid-stimulating hormone (TSH) is the first test ordered to understand how the thyroid gland is working. It is produced by the anterior pituitary gland and stimulates the production of thyroxine.

What TSH is and why it is measured

TSH is a glycoprotein hormone of the anterior pituitary gland. By acting on receptors of thyroid epithelial cells, it stimulates the production and activation of thyroxine, increases iodine uptake by the gland's cells, and triggers the biosynthesis of triiodothyronine (T3) and thyroxine (T4). There is an inverse relationship between free T4 and TSH concentrations: an elevated thyroxine level reduces TSH production, while a decreased level increases it. TSH secretion is regulated by the negative feedback system and hypothalamic releasing factors. The hormone is characterized by circadian fluctuations: the highest blood concentration is at 2–4 a.m., the lowest at 5–7 p.m. When awake at night, the normal secretion rhythm is disrupted.

TSH reference ranges in adults

With age, TSH becomes slightly higher, and the nocturnal hormone surge decreases.

TSH reference ranges in women: age, pregnancy, cycle

Thyrotropin concentration decreases during pregnancy. If you have hypothyroidism and are pregnant or planning pregnancy, you should inform your doctor: additional examinations will be needed. Untreated hypothyroidism increases the likelihood of serious pregnancy complications, including high blood pressure (preeclampsia), birth defects, premature birth, or miscarriage. No separate "female" TSH reference ranges outside of pregnancy and age are distinguished.

Thyroid hormone reference ranges: TSH, T4, and T3

Blood tests for the thyroid include TSH, T3, and T4, as well as a thyroid antibody test, which helps identify autoimmune diseases. Blood is not the only method: ultrasound, CT, thyroid scanning, and the radioactive iodine uptake test are also used.

• TSH — usually the first test ordered by a doctor
• T3 and T4 — show the level of thyroid hormones themselves in the blood
• Thyroid antibodies — markers of autoimmune disorders
• Ultrasound and scanning — assess the size, shape, and function of the gland

What affects TSH levels

Hormone concentration is affected by time of day (maximum at 2–4 a.m., minimum at 5–7 p.m.), age, pregnancy, and disruption of the nocturnal secretion rhythm when awake at night.

What elevated or decreased TSH means and when to see a doctor

With a deficiency of thyroid hormones, pronounced fatigue, cold intolerance, weight gain, constipation, difficulty concentrating, depressed mood, dry skin and hair, hoarseness, and irregular or heavy menstruation are possible. Symptoms develop slowly. If you suspect hypothyroidism, consult a doctor: they will ask about symptoms and family history, examine your neck, and if necessary order blood tests for TSH and T4. Untreated hypothyroidism or an incorrect medication dose is associated with risks to the heart and bones; in very rare cases, severe hypothyroidism leads to myxedema coma — an emergency condition requiring hospital treatment.

A TSH abnormality alone is not a reason to call an ambulance. Call 103 or 112 for life-threatening symptoms such as loss of consciousness, difficulty breathing, or chest pain.

This material is for reference: discuss the interpretation of results and further steps with your doctor.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer