Assessment of the concentration of osteoprotegerin and receptor activator of nuclear factor kB ligand in healthy children

Introduction
The OPG/RANKL ratio is an important determinant of bone mass and skeletal integrity, and it is also crucial in the pathogenesis of bone diseases. So far, few studies have been conducted to determine the reference values of OPG and RANKL in developmental age.

Aim of the study
The aim of the study was to determine the reference values of OPG, sRANKL concentrations and the OPG/RANKL ratio in healthy children, as well as to assess the impact of selected demographic factors and biological development on their concentrations.

Material and methods
Data obtained from medical records of 56 healthy patients aged 1–18 years were analyzed. Anthropometric measurements were analyzed for each child and the stage of puberty was assessed using the standard Tanner scale criteria. OPG and sRANKL levels were determined by ELISA with kits from Biomedica. The osteoprotegerin bioactivity index (OPG/RANKL ratio) was calculated for each patient by dividing OPG values by sRANKL (OPG/RANKL ratio).

Results
In the studied population of healthy children and adolescents, the OPG serum concentration reference value was established at 3.15–4.90 pmol/l, sRANKL at 0.20–0.60 pmol/l, and the OPG/RANKL ratio at 7.40–20.00. Serum OPG, sRANKL and OPG/RANKL levels did not change significantly with gender, BMI and Tanner stage of puberty. A statistically significant negative correlation was found between age and OPG levels (r = –0.32, p = 0.0168) and OPG/RANKL ratio (r = –0.34, p = 0.0228).

Conclusions
In healthy children and adolescents, OPG levels decrease with age, but the influence of puberty and body weight on OPG and sRANKL levels requires further investigation.