Interpreting the GnRH stimulation test in girls with central precocious puberty: the role of age and body mass index.

PURPOSE: The gonadotropin-releasing hormone (GnRH) stimulation test is the reference standard for diagnosing central precocious puberty (CPP), yet its reliability may vary with age and body mass index (BMI). This study evaluated the diagnostic performance of GnRH test parameters in girls with suspected CPP and examined the influence of age and BMI on their clinical interpretation.

METHODS

This retrospective study included 98 girls who underwent GnRH stimulation testing between January 2023 and December 2025 at a tertiary pediatric endocrinology center. Auxological data, basal luteinizing hormone (LH), stimulated LH at 40 min (LH₄₀), stimulated LH/FSH ratio (sLH/FSH), bone age advancement (BAA), and pelvic ultrasonographic measurements were recorded. Final CPP diagnosis based on longitudinal follow-up served as the reference outcome. ROC analyses, age- and BMI-stratified evaluations, and multivariable logistic regression were performed.

RESULTS

Thirty-six girls (36.7%) were diagnosed with CPP, and all initiated GnRHanalogue treatment. LH₄₀ showed the highest diagnostic performance (AUC = 0.738); a cut-off of 4.65 IU/L yielded 91.2% sensitivity and 61.7% specificity. Basal LH had limited accuracy (AUC = 0.668), and ultrasonographic parameters showed poor discrimination. LH₄₀ and BAA were independently associated with CPP. Diagnostic performance varied by age, with excellent discrimination in girls < 6 years (AUC = 1.000) and moderate accuracy at 6-8 years (AUC = 0.738). Increasing BMI was associated with reduced discriminatory capacity of LH₄₀, while uterine length showed relatively higher performance in girls with obesity.

CONCLUSION

The diagnostic performance of the GnRH stimulation test varied with age and BMI and was lower in older girls and those with obesity. LH₄₀ was the most informative hormonal parameter, but should not be interpreted in isolation. Test results should be integrated with clinical progression, auxological findings, skeletal maturation, biochemical data, and imaging when clinically indicated.