Thyrotropin

THYROTROPIN (TSH)

Thyrotropin (TSH), a thyroid-stimulating hormone, is produced in the pituitary gland, which is located below the cerebrum (see Thyroid hormone regulation, above). TSH stimulates the thyroid to secrete thyroxine (80–90 %) and, to a lesser degree, triiodothyronine (10–20 %). TSH is measured to determine the interaction between the central nervous system and the thyroid. An increase in TSH levels is detected in situations in which greater thyroid hormone production is required.

High TSH levels are indicative of subclinical hypothyroidism. High TSH coinciding with low free T3 and T4 hormones clearly indicates hypothyroidism. Elevated TSH levels may also indicate iodine deficiency. A decrease in TSH levels is caused by hyperthyroidism, excessive thyroid medication or pituitary gland and/or hypothalamus malfunction.

• Reference range: 0.5–3.6 mIU/L
• Optimal: 0.5–2.5 mIU/L