Serum Biochemical Markers of Bone Turnover in Healthy Infants and Children

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Abstract
Serum osteocalcin (OC), bone alkaline phosphatase (BAP), carboxyterminal propeptide of type I procollagen (PICP), carboxyterminal telopeptide of type I collagen (ICTP), parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D [1,25(OH)2D] were measured in 241 normal infants and children (134 males and 107 females aged 1.9 months-14 years, 1.8 months-12 years, respectively). Regarding the analysis of data for children above 2 yrs, we chose data with the following normalization: data/body surface x standard body surface, to eliminate biological variations not exclusively related to chronological age. The increase in serum OC occurred at the expected age of growth spurts in both sexes: in the first year of life OC values (mean ± SD) were 82.6 ±34.3 and 60.2 ± 32.9 OC ng/ml in males and females, respectively; during puberty, peak values occurred at the age of 10–12 yrs in girls (76.6 ± 25.8) and at the age of 12–14 yrs in boys (113 ± 48.3). Furthermore, significant positive correlations with age were found for males from 2 to 14 yrs (p < 0.00001) and for females from 2 to 12 yrs (p < 0.001). Elevated levels of BAP occurred in the first year, 70.4 ± 28.2 and 71.8 ± 28.5, and in the second year, 69.4 ± 26.7 and 67.4 ± 33.8 ng/ml, for males and females, respectively. For children older than 2 yrs, a positive correlation with age (p < 0.01) was found for females only, with a peak value of 67.2 ± 13.9 at the age of 10–12 yrs. For ages 2–14 yrs the reference values (mean ± 2SD) were 15.5 – 90.3 and 17.2 – 95.2 ng/ml for males and females, respectively. The highest PICP levels (1354 ± 680 ng/ml in males and 1041 ± 766 in females) were observed in infants less than 1 year of age, decreasing by about 60% at the age of 2. There was no significant change in serum PICP for children older than 2 yrs with values covering a range (mean ± 2SD) of 52 – 544 and 18 – 546 ng/ml in males and females, respectively. Similarly, the highest ICTP values were seen in infants younger than 1 year (29.7 ± 11.7 and 29.5 ± 20.1 ng/ml in males and females, respectively). In the ages from 2 to 14 yrs there did not seem to be any systematic age-correlated changes, with values covering a range (mean ± 2SD) of 6.06 – 24.5 in boys and 6.84 – 22.9 ng/ml in girls. Serum PTH concentrations (mean ± SD) in infancy were 27.2 ± 19.3 pg/ml for males and 25.8 ± 10.8 for females. Normal ranges (mean ± 2SD) in the older group were 5.77 – 53.1 and 6.71 – 57.3 pg/ml for males and females, respectively. Serum 1,25(OH)2D presented values of 47.3 ± 28.1 and 38.7 ± 18.2 pg/ml under 2 yrs for males and females, respectively. The ranges (mean ± 2SD) in children above 2 yrs were 9.5 – 101 pg/ml in boys and 10.9 – 88.4 in girls. The results of this study contribute to the establishment of reference values in normal children for these biochemical assays; these reference values are needed when the above biological markers will be applied in the monitoring of metabolic bone diseases.

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