ESPE Abstracts

Introduction: Precocious puberty (PP) is defined as the appearance of thelarche before the age of 8 years, in girls. The gold standard for the diagnosis is represented by the increase of LH level after stimulation with native GnRH, but a feasible alternative involves the administration of GnRH analogues. This test is poorly standardised and currently literature lacks of defined values to confirm the activation of the hypothalamic-gonadal axis, since they depend on the type of stimulus and on the methods used. Since 2002, in Verona, Italy, triptorelin has been used as analogous, with a LH cut-off of 15 IU/l measured 4 hours after the stimulus. Nevertheless, many girls have recently presented LH values below the cut-off despite signs of pubertal progression.

Aims: To identify a new threshold of LH post triptorelin stimulation to allow an earlier diagnosis of PP in girls with pubertal progression; to verify whether other parameters, such as the longitudinal diameter of the uterus, the bone age progression and estradiol levels after the assay, can be considered a valuable method to refine the diagnostic process.

Methods: We enrolled 186 females meeting the following criteria: thelarche onset between 4-8 years and GnRH analogue assay performed between 2015-2019 without showing any activation of the axis. 62 patients of this cohort repeated a triptorelin test due to a rapid clinical progression of puberty. The GnRH analogue assay was performed by injecting 100 mg/m² of triptorelin and measuring LH, FSH and estradiol levels before and four hours after the stimulus. All females underwent clinical evaluation, pelvic ultrasonography, and bone age.

Results: Patients presenting an activation of the axis at the second assay showed retrospectively significantly higher levels of post-stimulus LH at the first test when compared to those whose LH was inferior than 15 IU/l at the second test. They had significantly higher basal levels of LH, LH/FSH ratio and growth velocity. Statistical analysis led us to the identification of a new threshold for post-stimulus LH of 8.5 U/l (sensitivity: 83%, specificity: 76%, negative predictive value: 98%).

Conclusions: A post-stimulus LH value of 8.5 IU/l after triptorelin administration has been identified as the new cut-off to allow a diagnosis of PP in the early stages of hypothalamic-gonadal axis activation avoiding the repetition of the test for the progression of pubertal clinical signs. On the contrary, the other parameters analysed did not result conclusive for the diagnosis.