Random luteinizing hormone often remains pubertal in children treated with the histrelin implant for central precocious puberty.

To investigate the use of random ultrasensitive (US) luteinizing hormone (LH) levels to monitor children being treated with a histrelin implant for central precocious puberty (CPP). This was a prospective, uncontrolled, observational study at a pediatric endocrinology tertiary center. Thirty-three children (26 girls; mean age 7.2 ± 2.5 years) treated with a histrelin implant for CPP were enrolled. A random US LH measurement was obtained at 6 months, and a gonadotropin-releasing hormone analog stimulation test was performed at 12 months. Clinic visits occurred at baseline and at 6-month intervals. In 59% of the patients (17 of 29), the 6-month random US LH exceeded the prepubertal range of ≤0.3 IU/L. In contrast, gonadotropin-releasing hormone analog stimulation tests revealed complete hypothalamic-pituitary-gonadal axis suppression (peak LH <4 IU/L) in all 31 patients who underwent testing. US LH levels were highly correlated with peak stimulated LH levels. The mean peak stimulated LH level was higher in patients with a pubertal random LH than in those with a prepubertal random LH (1.2 ± 0.5 IU/L vs 0.5 ± 0.1 IU/L; P < .01). No patient had clinical evidence of pubertal progression. The random US LH level does not revert to a prepubertal range in more than one-half of patients with a histrelin implant and documented hypothalamic-pituitary-gonadal axis suppression. Long-term studies are needed to elucidate the optimal strategy for monitoring treatment in children with CPP.