Metabolic Bone Disease (Osteopenia of Prematurity)

Risk Factors & Pathogenesis

• Gestational age < 28 weeks or birth weight < 1000g (missing 3rd-trimester placental calcium/phosphorus dominant transfer).
• Prolonged TPN usage (> 4 weeks) lacking adequate Ca/P solubility limits.
• Chronic diuretic therapy (Furosemide highly increases renal calcium excretion).
• Prolonged postnatal corticosteroid use (Dexamethasone).
• Often asymptomatic until severe; presents late with unexplained fractures, craniotabes, or respiratory failure due to soft rib cage.

Screening & Biomarkers

• Screening starts at 4 weeks of age for at-risk infants.
• Serum Alkaline Phosphatase (ALP): > 800-1000 IU/L is highly predictive of demineralization (though bone and liver fractions are mixed).
• Serum Phosphorus: Consistently < 4.5 mg/dL indicates inadequate substrate.
• Tubular Reabsorption of Phosphate (TRP): Calculated value >95% strongly indicates phosphorus deficiency.
• Radiographs: Demineralization visible only after >20-40% of bone mineral is lost. Check for rickets-like changes at the metaphyses, or rib/long-bone fractures.

Nutritional Management Protocol

• Maximize Enteral Nutrition: Human Milk Fortifier (HMF) is strongly mandatory for breast milk up to 24-30 kcal/oz to provide Ca/P.
• Preterm formula (e.g., Neosure/Enfacare) naturally has higher Ca/P content than term formula.
• If on fluid restriction or TPN, aggressively maximize Ca/P within solubility curves.
• Vitamin D supplementation: Ensure 400-1000 IU/day total intake.
• Physical therapy: Daily gentle passive range of motion exercises (promotes bone mineralization via mechanical stress).

Diagnostic & Management Algorithm

• Metabolic Bone Disease Prevention: [START] VLBW infant -> [ACTION] Fortify breast milk / start preterm formula -> [MONITOR] Weekly Alk Phos & Phos -> [DECISION] Alk Phos > 800? -> [YES] Increase Ca/Phos supplementation

References

1. Abrams SA, Committee on Nutrition. Calcium and vitamin d requirements of enterally fed preterm infants. Pediatrics.