What is the normal range for serum thyroid-stimulating hormone?

The normal range for serum thyroid-stimulating hormone (TSH) is typically cited as being between 0.4 and 5.0 mU/L. This range is established based on extensive clinical research and is widely accepted in practice as it reflects the physiological levels of TSH in healthy individuals.

TSH plays a critical role in regulating the thyroid gland's production of hormones, which in turn control various metabolic processes in the body. When interpreting TSH levels, it is essential to consider that variations may occur due to factors such as age, pregnancy, and certain medications. Nonetheless, the value of 0.4-5.0 mU/L represents a conventional threshold where levels below may indicate hyperthyroidism (underproduction of TSH) and levels above may suggest hypothyroidism (overproduction of TSH), thus highlighting its clinical importance in the diagnosis and management of thyroid disorders.

Other ranges provided in the question, such as 1.0-3.0 mU/L, 5.0-10.0 mU/L, and 10.0-20.0 mU/L, fall outside the established normal limits, making them insufficient for representing normal TSH fluctuations in a healthy population.