After determining advanced bone age in a child with precocious puberty, which test helps differentiate between peripheral and central precocious puberty?

In cases of precocious puberty, distinguishing between central precocious puberty (gonadotropin-dependent) and peripheral precocious puberty (gonadotropin-independent) is essential for appropriate diagnosis and management. The test that is most useful for this differentiation is the measurement of LH levels before and after stimulation with GnRH.

When GnRH is administered, it stimulates the pituitary gland to release LH and FSH. In central precocious puberty, the pituitary gland is active, and there will be an appropriate rise in LH levels in response to the stimulation. This increase indicates that the precocious puberty is due to increased release of gonadotropins from the pituitary, confirming it as central precocious puberty. Conversely, if there is no significant increase in LH levels after GnRH stimulation, it suggests that the precocious puberty is of peripheral origin, where the sex steroids are produced independently of the pituitary gonadotropins.

This distinction is crucial as it influences management strategies; central precocious puberty often requires different therapeutic approaches compared to peripheral precocious puberty. Other tests such as testosterone or FSH measurements might provide additional information about the child's pubertal status, but they do not specifically address the central vs. peripheral cause as effectively as the LH