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Aims: We studied whether first morning voided (FMV) urinary gonadotropin measurements could be used as a noninvasive alternative to the GnRH test in the assessment of the hypothalamic-pituitary-gonadal function in children. Methods: In a single-center study, we compared FMV urinary gonadotropin concentrations with basal and GnRH-stimulated serum gonadotropin levels in 274 children and adolescents (78 girls, 196 boys) aged 5-17 years referred for growth and pubertal disorders. The concordance between FMV urinary gonadotropin concentrations and GnRH test results was assessed. Results: FMV urinary LH (U-LH), urinary FSH (U-FSH) and their ratios correlated well with the corresponding basal and GnRH-stimulated serum parameters (r = 0.66, p < 0.001). Receiver operating characteristic curve analyses using urinary and serum LH and FSH concentrations showed that FMV U-LH and U-LH/U-FSH performed equally well as the GnRH test in the differentiation of early puberty (Tanner stage 2) from prepuberty (Tanner stage 1) (area under the curve 0.768-0.890 vs. 0.712-0.858). FMV U-LH and U-LH/UFSH performed equally well as basal serum LH in predicting a pubertal GnRH test result (area under the curve 0.90-0.93). Conclusion: FMV U-LH determination can be used for the evaluation of pubertal development and its disorders, reducing the need for invasive GnRH stimulation tests. [ABSTRACT FROM AUTHOR]