Serial measurements of serum alkaline phosphatase for early prediction of osteopaenia in preterm infants

Aim: Osteopaenia commonly occurs in preterm infants; however, its diagnosis is often delayed when based on radiological findings. The aim of this study was to examine whether serial measurements of bone turnover markers are useful for early prediction of osteopaenia in preterm infants. Methods: Premature infants of ≤34 weeks gestation were enrolled. Serum alkaline phosphatase (ALP), bone form ALP (BALP), calcium and inorganic phosphate were concurrently measured biweekly from 3 weeks post‐natal age until 40 weeks post‐conceptional age. Radiographic examination of the forearm was performed at term age. Osteopaenia was defined as positive radiographic findings according to Koo's criteria. Results: Of the 46 premature infants completing the follow‐up study at term age, 18 showed osteopaenia in radiographic examination. Serum ALP was highly correlated with BALP (R² = 0.93, P < 0.001). Infants who had osteopaenia showed a higher level of ALP and BALP after 3 weeks post‐natal age than those who had no osteopaenia. ALP concentration exceeding 700 IU/L at 3 weeks post‐natal age was predictive of osteopaenia at term age (sensitivity 73% and specificity 73%) and so did for the predictive value of BALP concentration exceeding 95 ug/L (sensitivity 73% and specificity 80%). BALP measures provided no greater benefit of diagnostic performance than ALP in early detection of osteopaenia. Furthermore, premature infants with osteopaenia showed similar levels of calcium and inorganic phosphatase concentration compared with those without. Conclusion: Serum ALP concentration exceeding 700 IU/L at 3 weeks post‐natal age can predict the risk of osteopaenia in preterm infants.