Parathyroid hormone as a marker for metabolic bone disease of prematurity

Objective: To compare parathyroid hormone to alkaline phosphatase as a serologic marker for metabolic bone disease (MBD) in preterm infants. Study Design: An 18-month prospective observational study in neonates withbirth weight <1250 g. Simultaneous serum parathyroid hormone (PTH), alkaline phosphatase (ALP), calcium (Ca) and phosphorus (P) were measured at scheduled intervals during hospitalization. At 6 weeks of age, MBD was evaluated using knee radiographs. Comparisons were analyzed using multivariate logistic regression, receiver operating characteristic (ROC) curves, χ² and Student t-test.Result:Fourty-nine infants were included in the study: 7 with severe and 42 with mild MBD. Using ROC curves, at 660 U l^-1 ALP had a sensitivity of 29% and specificity of 93% for severe MBD, while a cutoff point of 180 mg dl^-1 gave PTH a sensitivity of 71% and specificity of 88%. Infants with severe bone disease had a lower birth weight, 21-day serum P, an increased use of glucocorticoids and caffeine, and more likely to have major neonatal morbidities.Conclusion: PTH is an early marker with better sensitivity than ALP in screening for MBD. At 3 weeks chronologic age, a PTH level >180 mg dl^-1 or a P level <4.6 mg dl^-1 yielded a sensitivity of 100% and specificity of 94% for severe MBD.