OSTEOCALCIN, SKELETAL ALKALINE-PHOSPHATASE, AND BONE-MINERAL CONTENT IN VERY-LOW-BIRTH-WEIGHT INFANTS - A LONGITUDINAL ASSESSMENT

Serum osteocalcin (Gla) and skeletal alkaline phosphatase (SAP) concentration both reflect osteoblast activity in the dynamic process of bone formation. To assess the relation in premature infants between change in bone mineral content (BMC) and both Gla and SAP serum concentration, we longitudinally measured BMC via photon absorptiometry and serum Gla and SAP concentration from birth to 16 wk in 20 very low birth weight infants. Serum total calcium, phosphorus, parathyroid hormone, and vitamin D metabolite concentrations were also monitored. All serum values were measured in the 20 mothers at delivery. Cord blood Gla concentrations were significantly (p < 0.03) greater than maternal levels, and by 1 wk had significantly (p < 0.001) increased from birth values. Total calcium, parathyroid hormone, phosphorus, and vitamin D concentrations remained in the normal range throughout the study. The increase in serum Gla concentrations, birth to 1 wk, were significantly correlated with the simultaneous increase in 1,25-dihydroxyvitamin D concentrations. The correlation between the change in BMC, however, over the first 4 mo of life and both Gla and SAP serum concentrations failed to reach statistical significance. Finally, a significant (p < 0.003) negative correlation was measured between serum Gla and SAP concentrations at wk 4, and, although not significant, a consistently negative correlation was measured from 1-16 wk of age. These data demonstrate a 1,25-dihydroxyvitamin D associated rise in neonatal serum Gla concentration during the 1st week after delivery, no significant correlation between the change in neonatal BMC over the first 4 mo of life and serum Gla or SAP concentration, and a consistent negative correlation between serum Gla and SAP concentrations. These data do not indicate that either serum Gla or SAP concentration is a reliable predictor for the change in bone mineral content of very low birth weight infants over the first 16 wk of life.