Abstract 32

In certain pubertal alterations the biochemical identification of the activation of the hypothalamic-pituitary-gonadal axis continues to be problematic, and, traditionally, different stimulation tests have been used. Aim: to study a normal pediatric and adolescent female population using ultrasensitive methodology, and to analyse by means of sensitivity (S), specificity (Sp) calculations and ROC plot different variables which could be used to distinguish between prepubertal and pubertal subjects. Clinical material: 148 ♀ (chronological age: 2.0-19y). Forty seven subjects corresponded to Tanner (T) I, 13 to T II, 13 to T III, 28 to T IV and 47 to T V. Methods: LH (mIU/ml) was measured by IFMA-Spec, FSH (mIU/ml) by IFMA and Estradiol by RIA. In each case, the LH-Spec/FSH ratio was calculated. The ROC methodology was applied to LH, FSH and LH/FSH results, with prepubertal values being interpreted as true positives. Results (range): Table Overlapping with T I is observed in LH-Spec=5/13 of T II, 1/28 of T IV and 2/47 of T V; in LH/FSH=8/13 of T II, 2/13 of T III, 1/28 of T IV and 1/47 of T V. The ROC plot analysis showed for LH/FSH ratio an optimal cutt-off at 0.15 (S: 90%, Sp.: 96%) that would make it possible to define prepubertal females with 90% probability (predictive value). On the other hand, a cutt-off at 0.40 would increase the probability of defining all the prepubertal population. (S: 100%; Sp: 84%). For LH-Spec the optimal cutt-off would be 0.30 mIU/ml (S: 93%; Sp: 95%). while a cutt-off at 0.70mIU/ml (S: 100%; Sp: 92%) would define all prepubertal subjects with a predictive value of 85%. FSH did not show any acceptable threshold. Conclusions: *In females the LH-Spec basal measurement and the calculation of the LH-Spec/FSH ratio made it possible to establish with a high predictive value, a cutt-off line to distinguish between prepuberty and puberty. *The use of this methodology in different pathologic situations would validate its use as a simples and efficient diagnostic resource.

Table 1 No caption available.
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