To determine the best cutoff value on the leuprolide stimulation test for the diagnosis of central precocious puberty (CPP) in a Brazilian population.

This observational study included 60 girls with CPP, as shown on the basis of serum concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) before and 3 hours after subcutaneous administration of 500 μg leuprolide acetate and by measuring serum estradiol concentrations 24 hours later. Six months later, each subject was clinically evaluated to determine whether she had experienced progressive or nonprogressive puberty.

Analyzing the best cutoff for LH after subcutaneous administration of 500 μg leuprolide acetate.

The best cutoff was a 3-hour LH level of greater than 4.0 mIU/mL, providing the highest sensitivity (73%) and specificity (83.1%), whereas a 3-hour LH level greater than 8.4 mIU/mL had a specificity of 100%. A 24-hour E2 concentration greater than 52.9 pg/mL had a sensitivity of 68% and a specificity of 74%. There was no association between pubertal development and disease progression. Signs such as thelarche and pubarche did not determine the evolution of the disease (P = .17). Clinical condition was associated with bone age/chronological age (P = .01), basal LH (P < .01), 3-hour LH (P = .02), baseline LH/FSH indices (P < .01) and after 3 hours (P < .01), and E2 at 24 hours (P = .02).

The optimal parameter indicating hypothalamic–pituitary–gonadal axis activation in our sample was a 3-hour LH level greater than 4.0 mIU/mL. A diagnosis of CPP, however, should be based on a set of criteria and not on an isolated measurement, because typical laboratory findings associated with CPP may not be present in all patients.