Thyroid-Stimulating Hormone (TSH): Function, Normal Levels, and Diagnostic Significance
Thyroid-Stimulating Hormone (TSH) is a vital biologically active substance produced in the pituitary gland that stimulates the thyroid gland’s function. It promotes the synthesis of active thyroxine (T4) and triiodothyronine (T3) hormones, as well as the growth of thyroid gland cells. The concentration of TSH depends on the levels of thyroid hormones in the body and is regulated by a negative feedback mechanism (as T3 and T4 levels increase, TSH secretion decreases, and vice versa).
Elevated or decreased levels of TSH can indicate irregularities in the thyroid gland axis, which includes the thyroid gland, pituitary gland, and hypothalamus. To determine the cause of deviation in TSH levels, comprehensive testing is required.
Here are the normal reference ranges for TSH levels:
| Age | Reference Range for Males (microIU/mL) | Reference Range for Females (microIU/mL) |
|---|---|---|
| Less than 1 year | 0.88-5.42 | 0.88-5.42 |
| 1-11 years | 0.67-4.5 | 0.66-4.75 |
| 11-15 years | 0.58-3.59 | 0.47-4.13 |
| Over 15 years | 0.35-4.94 | 0.35-4.94 |
Please note that TSH levels during pregnancy vary according to trimesters:
- First trimester: 0.1-2.5 microIU/mL
- Second trimester: 0.2-3 microIU/mL
- Third trimester: 0.35-3 microIU/mL
Analytical Results:
- High TSH levels may indicate various forms of hypothyroidism, lung or breast tumors secreting thyrotropin, pituitary gland tumors, thyroid cancer, or tissue resistance to thyroid hormones.
- Low TSH levels may occur due to hyperthyroidism, autoimmune thyroiditis, excessive intake of thyroid hormone-containing medications, pregnancy, pituitary gland injury, severe stress, hunger, or reduced thyroid and pituitary function.
Additional Tests:
- Measurement of thyroid hormones T3 and T4.
- Ultrasound examination of the thyroid gland.
- Consultation with an endocrinologist for result interpretation and treatment planning.
TSH is also known by other names, including Thyrotropin, Thyroid-stimulating Hormone, and Thyrotropin.
Indications for Analysis:
- Symptoms of hypo- or hyperthyroidism.
- Enlargement of the thyroid gland detected during physical examination or ultrasound.
- Abnormal T3 and T4 hormone levels.
- Infertility or ovulation issues in women.
- Hormonal imbalances affecting menstrual cycles, muscle weakness, hair loss, or depression.
- Delayed mental or sexual development in children.
- Monitoring thyroid diseases during treatment.
Blood samples for TSH analysis are typically collected along with thyroid hormone level tests to provide a comprehensive assessment of thyroid function. It’s advised to fast for 6 hours before the test and avoid strenuous physical activity, alcohol, and smoking. Results should be interpreted in consultation with a healthcare professional, considering individual circumstances and medical history.