A 16-year-old boy with no signs of puberty; Which hormone measurement would determine whether low testosterone is due to lack of pituitary stimulus?

A 16-year-old boy with no signs of puberty; Which hormone measurement would determine whether low testosterone is due to lack of pituitary stimulus?

• A. Estrogen
• B. Luteinizing hormone
• C. Follicle-stimulating hormone
• D. Adrenocorticotropic hormone

Answer: (B)

Key concept: the pituitary-gonadal axis controls testosterone via LH. LH, released by the anterior pituitary in response to GnRH, directly stimulates Leydig cells to make testosterone. If a teenager has low testosterone, checking LH shows whether the pituitary is providing the needed stimulus. Low LH with low testosterone points to a lack of pituitary (central) drive. If LH were high with low testosterone, the problem would be at the testicular level, not the pituitary. Thus measuring LH directly assesses pituitary involvement in the testosterone deficiency.

Key concept: the pituitary-gonadal axis controls testosterone via LH. LH, released by the anterior pituitary in response to GnRH, directly stimulates Leydig cells to make testosterone. If a teenager has low testosterone, checking LH shows whether the pituitary is providing the needed stimulus. Low LH with low testosterone points to a lack of pituitary (central) drive. If LH were high with low testosterone, the problem would be at the testicular level, not the pituitary. Thus measuring LH directly assesses pituitary involvement in the testosterone deficiency.