Quantification of urinary gonadotropins by specific assays may improve the evaluation of sex-specific hormonal changes in early infancy

Objective

The aim of this study was to investigate the feasibility of different gonadotropin assays for determining total and intact luteinizing hormone (LH), and follicle-stimulating hormone (FSH) immunoreactivity in urine (U-LH-ir and U-FSH-ir, respectively) during early infancy.

Design, Patients and Measurements

Morning urine samples were obtained from 31 infants, aged between 0 and 6 months, to study the age-related course of urinary gonadotropins. Additionally, we investigated bi-hourly urine samples of a 5-day-old male neonate for 24 h to observe the course of urinary gonadotropins during a daily cycle. We employed different immunofluorometric assays for measuring total and intact U-LH-ir, and U-FSH-ir.

Results

In neonates up to 21 days of age, the U-LH-ir levels measured by the regular LH assay (also detecting hCG) were significantly higher than those determined by the total (specific) LH assays (p = .004). U-FSH-ir was higher in girls than boys during both the first and the next 5 months (p = .02 and p < .001, respectively), whereas total U-LH-ir was higher in boys until 6 months of age (p < .001). Total U-LH-ir/U-FSH-ir ratio was significantly higher in boys than girls across the first half-year (p < .001).

Conclusions

The assessment of total U-LH-ir and U-FSH-ir, and their respective ratio constitutes a noninvasive, practical and scalable tool to investigate sex-specific changes during early infancy, with the ratio being significantly higher in boys than girls. Only highly specific LH assays detecting beta-subunit and its core fragment in addition to intact LH should be used for determining U-LH-ir in the neonatal period to avoid potential cross-reactivity with hCG of placental origin.