Serum luteinizing hormone concentrations increase 100-fold in females from 7 years to adulthood, as measured by time-resolved immunofluorometric assay.

The increases in serum immunoreactive (RIA) LH and FSH concentrations during puberty are small and of limited value in the evaluation of pubertal development. We, therefore, used highly sensitive time-resolved immunofluorometric assays to evaluate the changes in LH and FSH during female puberty. The sensitivity of the LH assay was 0.02 IU/L, and that of the FSH assay was 0.01 IU/L. Fifty normal premenarcheal girls, 7-12 yr old, 15 postmenarcheal girls, 16 to 17 yr old, and 15 adult women, 24-29 yr old, were studied. In postmenarcheal women, the blood samples were taken on cycle days 4-7. Serum estradiol concentrations were measured by RIA, and pubertal stages were graded. Serum LH levels in prepubertal girls were very low; the mean concentration was 0.05 IU/L. All girls less than 10 yr of age had serum LH concentrations below 0.2 IU/L, while FSH levels varied from 0.3-2.0 IU/L. The earliest significant changes in serum LH, FSH, and estradiol levels took place simultaneously at 9-10 yr of age. The increase in serum FSH was gradual, but the increase in serum LH was sudden and very steep, coinciding with the increase in serum estradiol and the onset of physical puberty. The increase in the mean LH concentrations between the 7-yr-old and the adult group was 116-fold, that for estradiol was 12-fold, and that for FSH was 6.7-fold. These results suggest that the increase in serum LH is important at the onset of puberty, and LH concentrations are a sensitive indicator of pubertal development.