Bone and collagen markers in preterm infants: Relationship with growth andbone mineral content over the first 10 weeks of life

In a longitudinal study of 25 preterm infants, we have examined the relatio nship of bone-specific alkaline phosphatase (ALP), C-terminal propeptide of type I collagen (PICP), N-terminal propeptide of type III procollagen (P3N P), C-terminal telopeptide of type I collagen, urinary pyridinoline (Pyd) a nd deoxypyridinoline (Dpd), with rates of gain in weight, length, and lower leg length and with bone mineral content (BMC), all measured at weekly int ervals over the first 10 wk of life. Concentrations of all collagen markers were 10-fold higher than in older children. Each marker showed a distincti ve pattern of postnatal change, with early increases in PICP and P3NP and d ecreases in ICTP reflecting postnatal growth. Once markers had reached a pl ateau during weeks 4-10, P3NP was positively correlated, whereas Pyd and Dp d were negatively correlated with rate of weight gain (r = +0.44, -0.46, an d -0.40, respectively, p < 0.05). P3NP was also positively correlated with overall linear growth (r = +0.44, p < 0.05). PICP was strongly correlated w ith mean BMC (r = +0.63,p < 0.01) and with total BMC attained by the end of the study period (r = +0.81, p < 0.001). Bone ALP was positively correlate d with the rate of bone mineral accretion (r = +0.55, p = 0.01). We conclud e that the marker of soft-tissue collagen formation, P3NP, is a good marker for overall ponderal and linear growth in preterm infants, whereas the mar kers of collagen breakdown, Pyd and Dpd, have inverse relationships with we ight gain. The osteoblast markers, PICP and bone ALP, seem to be good surro gate markers for bone mineralization in preterm infants. Markers may provid e information on whole-body turnover of bone and collagen that is complemen tary to traditional physical measures of growth and bone mineralization.