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OBJECTIVE Intensive studies of oestrogen receptors have suggested extragonadal functions of oestrogen. However, the in vivo extragonadal functions of oestradiol remain unclear because of the lack of an adequate assay system at low concentrations. In this study, we assessed the usefulness of a new ultrasensitive assay for children.

METHODS Serum oestradiol was measured with an ultrasensitive assay (assayable concentration: 5– 1835 pmol/l: ESTR-US-CT, CIS biointernational, France). Intra- and interassay coefficients of variation at low concentrations (< 36·7 pmol/l) were 8·2 ± 6·8 (0·1–31·2)% and 8·3 ± 3·7 (7·5–12·9)%, respectively.

SUBJECTS Sera from 88 healthy children (55 males and 33 females; 1 month to 16 years old) and 31 patients who underwent gonadal suppression therapy were analysed.

RESULTS Age-related changes were observed in both sexes. Serum oestradiol concentrations in childhood decreased slightly compared to those in infancy, then increased at puberty. Most prepubertal children showed oestradiol concentrations lower than 36·7 pmol/l. A study on patients who underwent gonadal suppression therapy revealed oestradiol changes within low concentrations, depending on the stage of the therapy.

CONCLUSIONS The new assay was considered precise enough for the assessment of oestradiol secretion at low concentrations in childhood. Age-related changes in serum oestradiol suggested gonadal activity in the prepubertal period. This assay could be a powerful tool for investigating novel oestradiol functions in vivo.