Normal urine levels of the aminoterminal telopeptide of type I collagen (NTx) in premature newborns in the first week of life

: Urinary excretion of type I collagen cross-linked aminoterminal telopeptide (NTx) is a specific index of bone resorption. The Authors have studied urinary NTx concentrations in 60 urine samples of preterm infants, from 32 to 36 weeks of gestation, to evaluate the trend of the bone marker in the first week of life. Urine samples were collected at 1, 3 and 7 days of life. NTx was measured by ELISA (OSTEOMARK) and the values expressed in nmol Bone Collagen Equivalent (BCE)/mmol u-creatinine and the mean values (+/- 1 SD) were compared by ANOVA. NTx levels showed a progressive increase from 1 to 7 days of life in every group (P = 0.002 at 32, 0.040 at 33, 0.019 at 34, 0.010 at 35 and 0.000 at 36 weeks of gestation). Moreover, by comparing the mean values in every day (1st, 3rd and 7th) in the whole period under investigation, significant variations were noticed at 1 and 7 days (P = 0.045 and P = 0.021) and highly significant variation on the 3r day (P =0.000). We found a inverse relationship between gestational age and NTx concentrations, with significantly higher values in preterm infants of 32-34 weeks compared to those found in the following weeks of life and to those of full term infants. Preterm infants have a higher bone turnover rate that seems to be responsible of the major risk of osteopenia. In conclusion, the trend of NTx at different gestational ages reflects the peculiar balance of mineral metabolism. The unexpected interruption of nutritional supply and of mineral triggers the turbulent combination of processes of bone formation and especially of bone resorption, that becomes more evident as more premature is the delivery.