FSH is a glycoprotein dimer with alpha and beta subunits. The beta subunit is unique to FSH, while the alpha subunit is the same as in TSH, hCG, and LH. FSH plays a pivotal role in the development and regulation of both the male and female reproductive systems by acting on the FSHR which is predominantly expressed in granulosa and Sertoli cells.

FSH test may be ordered if a boy or girl appears to be entering puberty earlier or later than expected. High levels are associated with precocious puberty, while low levels may indicate a delay in sexual development.

The test may also be used to check for disease of the testes or ovaries, pituitary gland, or hypothalamus, an almond-sized area of the brain that links the nervous system with the hormone-producing endocrine system. FSH levels can also help doctors evaluate fertility issues and menstrual problems. In addition, elevated serum FSH may play a significant role in the evolution of bone loss and obesity, as well as contributing to cardiovascular and cancer risk.