Age-related course of urinary gonadotropins in children

Serum levels of LH and FSH are very low from about 2 yr of age to the onset of puberty, which is heralded by a very sharp increase in LH levels. We studied age-related changes in urinary gonadotropins in a total of 184 boys and girls of various ages. Urinary FSH and LH were measured by ultrasensitive time-resolved immunofluorometric assays. The detection limit was 0.015 IU/L for LH and 0.018 IU/L for FSH. We observed that after an initial drop following the first months of life, urinary LH levels stayed below 0.5 IU/L until age 9 yr in girls and below 1.0 IU/L until age 11 yr in boys, whereas mean urinary FSH levels remained below 3.0 IU/L until age 10 yr in girls and 12 yr in boys. During puberty, mean urinary FSH and LH concentrations increased to about 5 IU/L in boys and 10 IU/L in girls. This corresponds to a 5-fold increase in FSH in both sexes and a 50- to 100-fold increase in LH in boys and girls, respectively. These dynamic changes agree with previous reports regarding serum levels, suggesting that noninvasive urinary gonadotropin measurements can be a viable alternative to serum determinations in the evaluation of gonadotropin secretion during childhood and adolescence.