Serum Alkaline Phosphatase as a Biomarker for Skeletal Maturity Assessment and Growth Prediction in Individuals Aged 7 to 17 Years

This study explored the association between serum alkaline phosphatase (ALP) levels and skeletal maturity and assess its potential as a hypothesis-generating adjunctive biomarker. One-hundred fifty-one subjects aged 7 ‒ 17 years who underwent hand-wrist radiography and serum ALP blood tests on the same day were enrolled retrospectively. Skeletal maturity was assessed using a Skeletal Maturity Indicator system, and serum alkaline phosphatase levels were measured using enzymatic colorimetry. Kruskal-Wallis tests, Spearman’s correlation, and multinomial logistic regression examined the relationship between ALP, chronological age, and skeletal maturity classification. Serum ALP levels showed significant differences across skeletal maturity stages (p < 0.0001), with the highest levels observed at SMI stages 6 ‒ 8. No significant sex-based differences were found (p = 0.226), and serum ALP levels were not linearly correlated with chronological age (ρ = 0.018, p = 0.824). A multinomial logistic regression model combining age and ALP level yielded improved classification accuracy for skeletal maturity (McFadden R² = 0.601, accuracy = 82.1%) compared to age alone. These findings suggested that serum ALP may partially reflect physiological bone maturation, and could be considered as a supplementary reference for skeletal maturity assessment if interpreted alongside chronological age.