Urinary excretion of cross-linked N-telopeptides of type 1 collagen to assess bone resorption in infants from birth to 1 year of age

Objectives. To evaluate noninvasively bone resorption in infants and more specifically, to assess the accuracy of urinary collagen type 1 cross-linked N-telopeptide (NTX) excretion normalized to creatinine (NTX/Cr) in a spot urine sample as a reflection of daily NTX production in infants and to compute normative values for NTX excretion from birth to 1 year of age. Methods. NTX/Cr values obtained from a single spot urine sample were compared with daily urinary NTX excretion and NTX/Cr obtained in 24-hour urine collected from 8 hospitalized infants. Normative values for NTX excretion were collated with a cross-sectional study in 70 healthy French infants (42 boys, 28 girls) aged 0 to 374 days (weight: 2700-11 340 g; length: 46-76.5 cm) and free of diseases or treatments that could influence growth, bone mineralization, or renal function. Results. NTX/Cr values from single spot urine sample were significantly and linearly correlated with both daily NTX excretion (r = 0.783) and daily NTX/Cr (r = 0.952). In healthy infants, NTX excretion is low at birth, increases dramatically and significantly during the first 10 days of life, remains significantly elevated for approximately 3 months, and then decreases progressively to return to values similar to that observed at birth by 1 year of age. Conclusions. These data provide new insights regarding the use of spot urine analysis for assessing NTX excretion during the first year of life. The normative data demonstrate significant age-related variations in this marker, which probably reflect adaptation to extrauterine life and accelerated bone turnover in infancy and which should be considered for the interpretation of this noninvasive bone resorption marker in the clinical setting.