Serum bioactive follicle-stimulating hormone levels in girls with precocious sexual development.

We studied the serum immunoreactive (immuno) and bioactive (bio) FSH concentrations in 16 prepubertal children (1.3-9 yr old), 6 girls with premature thelarche (0.8-2 yr old), and 9 girls with central precocious puberty (2.5-9.3 yr old). The serum bio-FSH was measured by the granulosa cell aromatase bioassay. The basal serum bio-FSH levels were not significantly different in patients with central precocious puberty (6.4 +/- 1.5 IU/L), premature thelarche (7.5 +/- 0.5 IU/L), and prepubertal controls (4.4 +/- 0.7 IU/L). However, the peak responses of both serum immuno- and bio-FSH levels to iv GnRH were higher in patients with premature thelarche (immuno-FSH, 29.3 +/- 2.3 IU/L; bio-FSH, 100.7 +/- 12.2 IU/L) than in those with central precocious puberty [immuno-FSH, 17.5 +/- 3.1 IU/L (p less than 0.05); bio-FSH, 42.4 +/- 9.8 IU/L (p less than 0.01)]. This suggests that in children with premature thelarche, there is a predominant immuno- as well as bio-FSH response to GnRH. After 12 months of GnRH agonist therapy, both serum immuno- and bio-FSH levels were suppressed in patients with central precocious puberty. The differences in clinical presentation between central precocious puberty and premature thelarche cannot be explained by the differences in FSH bioactivity.