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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.

The Authors have studied urinary aminoterminal telopeptide of type I collagen (NTx), a bone catabolism marker of recent determination, by an enzyme-linked immunoassorbent assay (OSTEOMARK) in 80 urine samples of term healthy infants in the first 3 months of life. Highly significant variations have been compared in the whole period studied (P = 0.000). Levels of NTx increase significantly from 1 to 7 days of life, reaching a plateau that is kept until 45th day and then significantly decrease until 90th day, when, however, they result higher than the values reported in literature concerning older ages. The Authors conclude that even this bone catabolism marker is influenced, in the first week of life, by the particular phenomenology linked to the neonatal adaptation, and that, subsequently, shows a trend strictly linked to the bone turnover modifications throughout the faster stage of the growth.