Background Osteopenia of prematurity remains a significant problem in Neonatal Intensive Care. Biochemical markers including serum alkaline phosphatase, phosphate and calcium have informed diagnosis and management. Parathormone (PTH) is important in bone health and the axis is known to be mature in preterm infants. There is no documentation of the changes in PTH over time in preterm infants.
Method Babies born before 32 weeks gestation (mean 26 weeks) and weighing less than 1500 grams (mean 893±290) at birth were recruited. Serial measurements of serum PTH were made from 2 weeks of age and fortnightly to coincide with clinical samples for electrolyte and bone chemistry, until term corrected gestation or discharge. Paired samples were taken for urinary calcium and phosphate.
Results Data from the first fifteen babies is presented.
Using an ALP cut-off of 400 IU/L to define osteopenia, babies with increased ALP, tended to have a higher PTH (p = 0.07), with mean PTH>7.9 pmol/L being associated with bone disease. Hypophosphatemia (Phosphate<1.5 mmol/l), a known risk factor, was significantly associated with hyperparathyroidism (p = 0.005). PTH and TmP-GFR were inversely correlated. Plasma calcium remained unchanged and within normal range.
Conclusion Hypophosphatemia is often assumed to be secondary to nutritional deficiency or renal tubular immaturity. Our data suggests the hypophosphatemia is at least in part secondary to hyperparathyroidism. It is unclear whether this is a causal relationship with osteopenia or not. The potential benefit of PTH measurement in prediction of risk, diagnosis and management of osteopenia is highlighted.