Background and Objectives: bLH is considered an excellent biochemical predictor of CPP. However, its utilization in clinical practice shows some uncertainties. This study aims to evaluate the diagnostic power of bLH and propose a diagnostic algorithm for CPP. Materials and Methods: We conducted a monocentric cohort retrospective study evaluating all females referred for suspicion of CPP between 1 January 2017 and 31 December 2020 who underwent a GnRH test. Auxological, hormonal, and instrumental data were collected, including pelvic ultrasonography and bone age (BA) assessment. Simple linear regression, t-test, and ROC tests were utilized to study the diagnostic value of basal hormone levels. Two hundred thirteen girls were included in the study. They were subdivided into two groups according to the results of the GnRH test: Group 1, with LH peak > 5 IU/L (pubertal) and 79 patients (37%), and Group 2, with an LH peak ≤ 5 IU/L (prepubertal) and 134 patients (63%). Results: The ROC curve showed that bLH level > 1.5 Ul/L best predicts a pubertal response to the GnRH test (AUC 0.8821, accuracy 82%), with low sensitivity (34%). The multivariate analysis found that bLH > 0.5 IU/L, basal FSH (bFSH) > 3.5 IU/L, bLH/bFSH ratio > 0.16, BA advancement > 1.7 years, uterine volume > 3.6 mL, longitudinal uterine diameter > 41 mm, and the presence of endometrial rhyme were significantly associated with a pubertal response at the GnRH test. An algorithm based on these features was created, and its application would reduce the number of GnRH tests by 34%. Overall, 96.2% of Group 1 patients reached the LH peak at the 30th minute of the GnRH test, supporting the hypothesis that the GnRH test duration could be reduced to 30 min. Conclusions: Morning bLH > 1.5 IU/L could be carefully used as a diagnostic predictor of CPP. The GnRH test, even reduced to 30 min, could be reserved for girls who show low intermediate morning bLH and specific clinical signs of pubertal development.
Keywords: GnRH test; basal luteinizing hormone (bLH); central precocious puberty.