Outcomes of standardised approach to metabolic bone disease of prematurity

To assess the current protocol of metabolic bone disease (MBD) at three Monash Health neonatal units (Melbourne, Australia).

Retrospective audit of 171 infants born at <32 weeks' gestation over 18 months. Mean gestational age was 28.6 ± 2.1 weeks, and birthweight was 1190 ± 374 g. Risk factors of MBD include intra-uterine growth retardation (n = 33, 19.3%), maternal pre-eclampsia (n = 17, 9.9%), necrotising enterocolitis (n = 9, 5.4%) and medications like methylxanthines (94.2%; mean 54.8 days), diuretics (38.6%; mean 49.2 days) and glucocorticoids (5.3%; mean 35 days).

In total, 84.8% infants had an initial MBD screen (mean age 36.3 days), with 45% having repeated monitoring (mean age 71.9 days), and 14.2% had initial alkaline phosphatase levels >500 U/L, decreasing to 10.1% on follow-up. All infants received additional vitamin D supplementation of 400 IU/day, phosphate of 25.1% (n = 43) and calcium of 19.9% (n = 34). Fractures were identified from clinical documentation in 2.9% (n = 5) of infants. Stratifying into phosphate-treated and untreated groups revealed significant differences (P < 0.001) for gestational age and birthweight: 26.7 ± 1.7 weeks/918 ± 272 g for treated versus 29.2 ± 1.9 weeks/1283 ± 359 g for untreated. In the phosphate-treated group, improvement was seen in mean alkaline phosphatase (pre-treatment 467 ± 204 U/L and post-treatment 342 ± 221 U/L, P < 0.01) and mean phosphate levels (1.8 ± 0.4 vs. 2.2 ± 1.0 mmol/L, P < 0.01). Linear growth difference between phosphate-treated (n = 10) and untreated groups (n = 24) was insignificant at >6 months of age (P = 0.13), although this may reflect limited data.

Adequate first-line supplementation with vitamin D and phosphate appeared to improve biochemical markers of MBD, but given the observational nature of this study, further longitudinal/prospective studies are required to confirm these findings.