Urinary Calcium and Phosphorus Excretion in Vitamin D-Sufficient Preterm Infants: Establishing Age-Specific Normative...

Area of Science:

• Neonatal Medicine
• Pediatric Nephrology
• Nutritional Science

Background:

• Very low birth weight (VLBW) infants (<1500g) are at risk for metabolic bone disease.
• Methylxanthine treatment is common in VLBW infants, potentially affecting mineral balance.
• Understanding calcium and phosphorus homeostasis is critical for VLBW infant care.

Purpose of the Study:

• To evaluate urinary calcium (Ca) and phosphorus (P) excretion in VLBW infants without severe morbidity, treated with methylxanthines.
• To establish normative data for urinary Ca and P excretion in this population.
• To investigate the influence of vitamin D status on mineral excretion and homeostasis.

Main Methods:

• Analysis of urinary Ca and P and their creatinine ratios in 81 VLBW infants biweekly until day 56.
• Assessment of serum parathyroid hormone (PTH), 25-hydroxyvitamin D [25-(OH)D], total Ca, P, and alkaline phosphatase (ALP).
• Bone densitometry performed before discharge.

Main Results:

• Urinary Ca and P excretion differed significantly from their creatinine ratios.
• Vitamin D status influenced urinary mineral excretion, likely via PTH regulation, but not serum minerals or ALP.
• Normative data were established only for infants with sufficient vitamin D (>50 nmol/L).

Conclusions:

• Age-specific normative data for urinary Ca and P excretion in healthy, vitamin D-sufficient VLBW infants were provided.
• Urinary mineral excretion significantly varies with postnatal age, necessitating individualized monitoring.
• Sufficient vitamin D is crucial for calcium-phosphorus homeostasis, impacting Ca excretion and P levels from 2 months of age.