Estrogen levels in girls with premature thelarche compared with normal prepubertal girls as determined by an ultrasensitive recombinant cell bioassay

Objective: Estradiol levels in girls with premature thelarche have not previously been well defined because of the lack of adequate sensitivity of previously available estradiol assays. The ultrasensitive recombinant cell bioassay for estradiol has made the study of estradiol levels in premature thelarche possible. We hypothesized that girls with premature thelarche have higher estradiol levels than normal prepubertal girls. Study design: We used an ultrasensitive recombinant cell bioassay to study estradiol levels in 20 girls with premature thelarche and 15 normal prepubertal girls less than 3 years of age. The 2 groups were compared by Student t test. Results: Estradiol levels were significantly greater in the girls with premature thelarche (8.4 +/- 4.5 pmol/L estradiol equivalents) than in the normal prepubertal girls (3.3 +/- 3.5 pmol/L estradiol equivalents; P < .01). The estradiol level was not significantly correlated with age, height, weight, body mass index, age at onset of thelarche, or the presence or absence of ovarian cysts. Conclusion: Girls with premature thelarche have significantly higher estradiol levels than normal prepubertal girls. This is consistent with the hypothesis that the mechanism of premature thelarche involves increased estradiol levels rather than increased sensitivity of breast tissue to normal estradiol levels.