Endocrine Abstracts

Introduction: Metabolic bone disease of prematurity (MBDP) is a common condition in preterm and low birth weight infants, characterised by under-mineralisation of bone due to inadequate mineral supply, which can increase the risk of fractures. Screening is undertaken using biochemical markers, typically serum phosphate (PO4), alkaline phosphatase (ALP) and parathyroid hormone (PTH), although the objective clinical utility of these markers individually has not been explored.

Objective: To investigate the utility of the biochemical screening markers for MBDP by determining sensitivity, degree and timing of derangements.

Methods: All preterm infants admitted to a tertiary neonatal unit over a one-year period that had biochemical evidence of MBDP (at least one of: raised ALP, raised PTH and low PO4) with no other explanation for derangement were included, with the progress of their biochemistry tracked retrospectively.

Results: 59 preterm infants were included. The mean age for the first derangement of each marker was 23 days for ALP, 40 days for PTH, and 24 days for PO4. Peak derangement was noted earlier with PO4 (39 days) than PTH (65 days) and ALP (56 days). PTH demonstrated the greatest degree of derangement – average peak value 16.2 pmol/L (standard deviation 12.8, upper limit of normal 6.9). Sensitivity for predicting MBDP was 81% for ALP, 78% for PTH and 71% for PO4, with the greatest sensitivity achieved with a combination of raised ALP and PTH (98%). However, at the time of first screening for MBDP, sensitivity for predicting future derangements was 59% for ALP and PTH, and 39% for PO4. Earlier derangements were observed to ALP and PO4 than PTH, particularly in extremely preterm or extremely low birth weight infants.

Conclusion: Biochemical derangements of MBDP are noted from 3–4 weeks of life, suggesting that screening should commence from this point. A combination of PTH and ALP provides the greatest sensitivity for predicting MBDP.