The Diagnostic Utility of the Triptorelin Stimulation Test Compared to the Standard Gonadotropin-Releasing Hormone Stimulation Test in Children with Idiopathic Central Precocious Puberty

Background: Central precocious puberty (CPP) is diagnosed through a combination of clinical, auxological, and biochemical parameters, with pharmacological stimulation tests considered the diagnostic gold standard. In recent years, triptorelin, a long-acting Gonadotropin-Releasing Hormone (GnRH) analog, has been increasingly adopted in clinical practice due to limited availability of native GnRH. Objective: To compare the clinical, auxological, and hormonal profiles of girls diagnosed with idiopathic CPP using either the classical GnRH stimulation test or the triptorelin test. Methods: This retrospective study included 136 female patients diagnosed with CPP and followed for at least two years at a single pediatric endocrinology unit. Of these, 101 underwent a GnRH stimulation test, and 35 were assessed using the triptorelin test. Baseline and stimulated hormonal parameters, growth data, and IGF-1 levels were collected. A multivariate linear regression model was used to explore the influence of age, test type, and other covariates on the LH peak response. Results: Anthropometric and baseline hormonal parameters were comparable between the two groups. The LH peak was significantly higher in the GnRH group (9.8 ± 3.1 IU/L at 60 min) than in the triptorelin group (6.8 ± 2.4 IU/L at 4 h). FSH levels were also significantly lower following triptorelin stimulation (p = 0.004), while the LH/FSH ratio did not differ significantly. Multivariate analysis confirmed that triptorelin was associated with a lower LH peak (β = −2.2, p = 0.008), particularly in younger patients, with a significant interaction between age and test type (β = 0.6, p = 0.022). Conclusions: Both GnRH and triptorelin stimulation tests are valid tools for CPP diagnosis. However, the GnRH test appears to elicit a more robust LH response, especially in younger patients, whereas the triptorelin test is associated with delayed and lower LH peaks.