Endocrine Abstracts

JOINT689

Objectives: Metabolic bone disease of prematurity (MBDP) is characterized by skeletal undermineralization. The risk of MBPD increases significantly in infants born before completing 28 weeks of gestation or those with extremely low birth weight (ELBW; <1,000 g). The most common biochemical changes in MBDP include hypophosphatemia and hyperphosphatasemia. Serum phosphate levels tend to decrease earlier than the elevation of serum alkaline phosphatase (ALP). In this study, we aimed to investigate the optimal screening time and cutoff values of phosphate for MBDP screening.

Methods: We conducted a retrospective study of medical records from premature infants hospitalized in the neonatal intensive care unit (NICU) at Korea University Ansan Hospital between 2020 and 2023. Infants with gestational age <32 weeks or birth weight <1,500 g were included. Those who died or had incomplete data were excluded. MBDP was defined as a serum ALP level >900 U/l and serum phosphate below 5.5 mg/dl within the first 3–5 weeks of life. We evaluated serum calcium, phosphate, and ALP that measured every week, along with wrist radiographs at 6 weeks of age.

Results: A total of 95 infants were included in this study. Of these, 23 (24.2%) met the MBDP criteria. The prevalence rate of MBDP was 57.7% (15/26) in ELBW infants. The MBDP group had a significantly lower mean gestational age [26.8±2.2 weeks vs. 29.7±2.2 weeks, P<0.001] and lower mean birth weight [885.5±269.2 g vs. 1296.6±314.9 g, P<0.001]. The duration of TPN, establish of full feeds, caffeine use, and steroid use were longer in MBDP group: 30 (21-48) vs. 15.5 (10-23.5) days, 34 (21-51) vs. 15.5 (11-26) days, 74.0±26.9 vs. 40.0±27.2 days, and 10 (0-13) vs. 0 (0-0) days, respectively (P<0.001). Infants with MBDP had significantly higher serum ALP levels at 2 weeks [741.09±48.18 U/l vs. 516.26±27.23 U/l, P<0.001], and lower serum phosphate levels at 1 week [3.38±0.30 mg/dl vs. 4.07±0.17 mg/dl, P<0.001]. The optimal phosphate cutoff at 1 week was 3.85 mg/dl, with 70% sensitivity and 53% specificity. Wrist X-rays at 6 weeks revealed signs of rickets in 16 (69.6%) infants with MBDP, compared to 13 (18.1%) infants without MBDP (P<0.001).

Conclusion: Decreased serum phosphate levels in the first week of life were associated with an increased risk of developing MBDP. Since phosphate levels decline earlier than ALP levels rise, meticulous monitoring of infants with low phosphate levels in the first week of life is necessary for early detection and intervention.