P2C374: The Effect of Gestational Age on Serum Alkaline Phosphatase Levels in Premature Infants Born at ≤32 Weeks

Background: Osteopenia of prematurity (OPP) is a co-morbidity of prematurity related to poor calcium and phosphorous intake and high bone mineralization and growth. OPP incidence varies from 23-30% among premature infants born ≤ 1500 grams. Initial serum total alkaline phosphatase (ALP) > 500 mg/dl is considered abnormal. Periodic measurements of ALP, calcium and phosphorus are used to monitor OPP and to optimize dietary supplementation. However, the relationship of ALP to gestational age at time of measurement, i.e. Corrected Gestational Age (CGA = birth-GA + age after birth in weeks), it not well documented.

(i) Evaluate the relationship between ALP and CGA at the first measurement in premature infants born at ≤32 wk GA; and (ii) evaluate factors associated with ALP levels >500 mg/dl

Methods: Retrospective data from the Connecticut Children’s NICU at UCONN Health were collected for admissions between Sept 2018 to Dec 2021 for infants born ≤32 wk GA. During this period, routine ALP levels were done within 2-4 weeks of birth to evaluate risk for OPP during which time most infants had transitioned from IV to full enteral nutrition with human milk. After excluding Infants with congenital bone or endocrine disease, genetic syndromes, and GI abnormalities, we evaluated all infants whose first ALP measurement was done within 4 wks of birth. First measured ALP levels were correlated to CGA at the time of measurement. Demographic and potential confounding data were also aggregated. Infants were grouped into 4 CGA categories. Group 1: 24-28 wk, Group 2: 29-31 wk, Group 3: 32-34 wk and Group 4: ≥ 35 wk. Univariate and multivariate comparisons were made using SPSS v29 software.

Results: Of 200 infants who survived during the study period, 176 infants had their first ALP done at 2 ± 0.5 wk (mean±sd). There was a negative correlation between CGA and ALP with R2 = 0.181, p< 0.001.(Figure 1) We found a significant association of abnormal ALP (>500 mg/dl) with lower BW and GA at birth. There were no significant associations with maternal age, infant sex, race, singleton births, or initial serum Ca and P levels. (Table 1) ANOVA analysis showed that lower CGA groups (Groups 1 and 2) had significantly (p < 0.02) higher ALP than higher CGA groups (Groups 3 & 4). The significant relationship persisted after correcting for birthweight (BW) but the effect of other variables was not significant.

Conclusion: ALP within 4 weeks after birth is primarily correlated with CGA but not birthweight or serum Ca and P levels. GA-based normative data of the first ALP are important in monitoring premature infants for OPP and instituting early therapy. The effect of therapies such as vitamin D, mineral supplements, diuretics, and steroids on changes in ALP levels remains to be evaluated.