Diagnostic utility of basal luteinizing hormone in evaluating central precocious puberty

Background: Basal luteinizing hormone (bLH) is increasingly proposed as a surrogate marker of hypothalamic-pituitary-gonadal activation, potentially reducing the need for gonadotropin-releasing hormone (GnRH) testing in children with suspected central precocious puberty (CPP). However, diagnostic thresholds remain assay-dependent, and values below the detection limit complicate interpretation. Objective: This study aims to assess the diagnostic performance of bLH in predicting GnRH test response in patients evaluated for suspected CPP, using a censoring-aware approach for values below the assay limit of detection (LOD). Methods: We retrospectively analyzed 258 first-time GnRH stimulation tests performed for suspected CPP between 2011 and 2025 at the Royal Hospital for Children and Young People, Edinburgh. Basal luteinizing hormone was measured in fasting early-morning samples collected between 08:00 and 10:00 Am immediately before GnRH administration, with Abbott Architect (LOD 0.5 U/L) or Roche Cobas (LOD 0.3 U/L). Values below the assay-specific LOD were treated as left-censored observations and handled with parametric regression on order statistics. Receiver operating characteristic analyses were performed separately by sex. Results: Basal luteinizing hormone showed good accuracy for predicting a pubertal GnRH response, with an AUC of 0.80. The optimal threshold was 0.5 U/L (sensitivity 0.61, specificity 0.97), while a bLH ≥ 1.0 U/L achieved 100% specificity and positive predictive value. Sex-stratified analyses showed similar performance in girls and boys, although discrimination was higher in boys. Combined models including bLH and sex steroids did not materially improve discrimination in girls, whereas the model combining bLH and testosterone showed strong performance in boys (AUC 0.88). Conclusion: Early-morning bLH provides clinically useful information for the assessment of suspected CPP. Higher values can reliably predict a positive GnRH response, supporting its use as a first-line test and a more selective use of GnRH stimulation testing, whereas low or indeterminate values still require careful clinical interpretation.