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 prev iously been well defined because of the lack of adequate sensitivity of pre viously available estradiol assays. The ultrasensitive recombinant cell bio assay for estradiol has made the study of estradiol levels in premature the larche possible. We hypothesized that girls with premature thelarche have h igher 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 prepube rtal 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 prem ature thelarche (8.4 +/- 4.5 pmol/L estradiol equivalents) than in the norm al prepubertal girls (3.3 +/- 3.5 pmol/L estradiol equivalents; P < .01). T he estradiol level was not significantly correlated with age, height, weigh t, body mass index, age at onset of thelarche, or the presence or absence o f ovarian cysts. Conclusion: Girls with premature thelarche have significantly higher estrad iol levels than normal prepubertal girls. This is consistent with the hypot hesis that the mechanism of premature thelarche involves increased estradio l levels rather than increased sensitivity of breast tissue to normal estra diol levels.