ORF47-03 - Bone-Specific Alkaline Phosphatase vs. Its Z-Score as Complementary Diagnostic Markers for the Assessment of Children and Adolescents with Secondary Osteoporosis

Introduction: The role of bone-specific alkaline phosphatase (BsALP) as a predictor of primary osteoporotic status and treatment efficacy has been studied in adult patients. However, due to the dynamic nature of bone turnover in children and adolescents, its applicability in the pediatric population remains unclear. This study compares the predictive value of age- and sex-matched BsALP Z-score versus the absolute BsALP value for bone mineral density (BMD) in children and adolescents with secondary osteoporosis.

Methods: We retrospectively analyzed 290 post-pubertal males (aged 12.5-18 years) and females (aged 10.5-18 years) with underlying hemato-oncologic, rheumatologic, gastrointestinal, endocrinologic, or other chronic conditions. Lumbar spine and femoral BMD Z-scores were measured using dual-energy X-ray absorptiometry. Serum BsALP levels were obtained, and their Z-scores were calculated based on the mean and the 0.05 and 0.95 centiles across eight age groups. Associations between BsALP and BsALP Z-scores with lumbar spine BMD (LSBMD), low bone mass (LSBMD Z-score ≤-2), and vertebral fracture (VF) were evaluated.

Results: 103 were male (35.5%), with a mean age of 15.3±2.08 years. The mean LSBMD Z-score was -0.61±1.32, and 13.8% had low bone mass. In multivariate linear regression, both BsALP (β = -0.005, p = 0.021) and BsALP Z-score (β = -0.176, p = 0.014) were associated with LSBMD. Logistic regression showed that the BsALP Z-score was more strongly associated with low bone mass (OR = 7.92, p = 0.003) and VF (OR = 3.67, p = 0.001) compared with the absolute BsALP value (low bone mass: OR = 1.08, p = 0.003; VF: OR = 1.05, p < 0.001) after adjusting for underlying disease, age, sex, and BMI Z-score.

Conclusion: In children and adolescents with secondary osteoporosis, the BsALP Z-score demonstrates stronger and more consistent associations with low bone mass and VF than the absolute BsALP value. BsALP Z-score may serve as a valuable serum indicator for identifying pediatric patients at risk for bone fragility.

Keywords: bone density, osteoporosis, bone remodeling, pediatrics