The normal values for serum INHB have been often assessed among adults, especially fertile and infertile adults14–16. However, few study has established sex- and age-related INHB reference data from birth to adulthood (n = 366, boys)5, aged 6-11years (n = 705, girls)6 and during childhood and puberty (n = 52, girls)13 in European and western countries. Due to the practical difficult in infant’s recruitment, some studies may contain few infants or participants aged range of 5 ~ 18 years old. In the current study, 163 infants (< 1 y subgroup) were regarded as a key strength of our study. To the best of our knowledge, this is the first one to detect serum INHB concentrations in heathy children aged from 0 to 18 years among a large group of more than 600 populations in China. In this study, we investigated the age- and gender-related effects on INHB concentrations and calculated the pediatric RIs from birth to puberty based on a newly introduced fully automatic chemiluminescence analyzer.
Our results suggested that gender and age had effects on INHB levels. The level of INHB for boys and girls was similar U-shaped along with age and the optimal estimated models both were cubic. The distribution of INHB levels as four age groups also confirmed the shaped phenomenon. Our finding suggested that INHB was highly variable during the first year of life and attained gradually stability as the age, then increase to adolescence. INHB for girls was high from born, and decreased gradually to reach a trough at 2 ~ 8 years old, and then increased again to reach a crest around 13 years old. However, there were differences for boys, with step to plateau level around 5.5 ~ 9 years old and a crest around 13 years old, which were similar trends with previous study5. Increase of INHB at infants and pubertal period were involved the Sertoli cell proliferation17, 18, which in males within one year old can increase fivefold17.
We found the post-natal peak exceeded the level of INHB in pubertal period in boys. Andersson et al also observed that the peak in infant boys exceeded in adult men 19. High level of infancy affords an early opportunity to assess hypothalamic-pituitary-gonadal axis function, which is urgently needed, especially, when newborn happens ambiguous genitalia or suspicion of hypopituitarism or hypogonadism20. Postnatal increase of INHB also may predict later testicular function, such as spermatogenesis, but abundant studies are requested to evaluate its effectiveness21. Our study also showed that INHB raised from age 8 for girl and 9 for boys, which seem to be early than the clinical onset of puberty with mean age of 9 years in girls and 11.5 years in boys, respectively. This demonstrates that INHB secretion takes places in the prepubertal testis, despite the very low levels of both gonadotrophins and TT. Therefore, INHB is used to assess Sertoli cell health and number in pre-pubertal stage.
Interestingly, our finding showed that girls not only had lower concentrations but also reduced variability in INHB across four age groups compared to the boys. These results were in agreement with previous studies at all stages of puberty22 and in infancy20. Besides INHB, anti-Müllerian hormone is also expressed at varying degrees in children23. However, no published study investigated detailed the difference variability of INHB for girls and boys with different age groups in healthy pediatric populations.
The INHB reference ranges have changed over the years in adults among different laboratories24. Further, previous reports showed that INHB level was U-shaped with age from birth to adulthood5. So, this prompted us to reconsider the INHB cutoff value in childhood and adolescence. Because INHB concentrations in different sex and age individuals were significant difference, the age-specific and sex-specific RIs were calculated separately.
Our RIs for INHB [236(75–476) pg/ml for < 1y; 102(53, 265) pg/ml for 5 ~ 10y] was close to the ranges observed in children of the same age range in Ireland [278(68–630) pg/mL for < 1y, n = 51; 84 (35–167) for 6 ~ 10y, n = 80]5. However, our RIs for INHB at 10 ~ 18 group [156 (54, 290)] pg/mL was different from the 12 ~ 17 y group [280 (74 ~ 470) pg/mL in Ireland5. The remarkable difference of RIs may result from study populations, the establish criteria of reference range, and detection methodologies24.
Our study indicated that INHB levels were correlated positively with FSH and LH in girls, which were consistent with previous reports in prepubertal, pubertal girls 22. Other studies also showed no association between FSH and INHB in prepubertal cryptorchidic boys (0.5 to 13 year)25 and normal prepubertal boys5. Our study showed that serum INHB moderately correlated positively with E2 (P = 2.52×10− 9) and negatively with PROG (P = 0.028) in girls. INHB correlated positively with PRL (P = 8.91×10− 7) levels in boys. However, we did not find any reports on correlations between INHB and E2, PROG, and PRL in children.
There are several limitations in our study. Firstly, although the inclusion criterion were standardized to select possibly those healthy individuals, it is possible to include pathologic subjects. Secondly, due to certain practical limitations, the participants in adolescence were not identify as Tanner staging and menstrual cycle. Finally, we do not evaluate INHB level in repeated measures.
In conclusion, our study administrated the age- and sex-dependent RIs for serum INHB. Our results suggested that INHB level was lower and reduced variability for girls across four age groups compared to boys. INHB concentration changed along with age. Furthermore, significant difference for correlations between INHB and FSH, LH, E2, PROG, PRL were observed in different sex. Our results may broaden the application of INHB levels, which may be sensitively used as an effective indicator of gonad function assessment and distinguish the patients and normal children.