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Technical Briefs |
Ist. di Patol. Generale e Oncol., Seconda Univ. degli Studi di Napoli, Larghetto S. Aniello a Caponapoli, 2, 80138 Napoli, Italy;
a author for
correspondence: fax +81/566-5695
Osteocalcin or bone Gla protein (BGP) is a vitamin K-dependent,
low-molecular-mass (5800 Da), 49 amino acid peptide synthesized by
osteoblasts (1)(2). Osteocalcin contains three
residues of 
-carboxyglutamate, which provide the point of
interaction between the BGP and hydroxyapatite in the extracellular
bone matrix. The 19–20 and 43–44 residues provide sites for the
tryptic hydrolysis; the resulting peptides may be the products of
liver, kidney, and plasmatic breakdown of the molecule. The
physiological role of these fragments is unknown.
Osteocalcin is an important marker of bone turnover in physiological and pathological conditions (3). Physiologically, serum osteocalcin was increased in children, particularly during the first year of life and during puberty, when the evolution of the concentration was related to the rapidity of physical growth. The significant correlation between BGP and testosterone and serum insulin-like growth factor 1 is consistent with the important role of this protein in the skeletal growth (4). Some authors have reported a decrease of serum osteocalcin in growth hormone-deficient children and normalization after hormone treatment (5)(6). The aim of this study was to determine serum osteocalcin in a large group of children according to their age.
We selected for recurrent controls for the study 1634 healthy children (801 girls, 833 boys), ages 1–16 years, arriving at the Department of Paediatrics. None of the subjects was receiving any medication and all were ambulatory. All children with evidence of endocrine, hepatic, renal, or other diseases known to affect bone metabolism were not considered. A single venous blood sample was obtained and the serum was extracted and frozen until assay. The procedures followed for human investigations were according to the ethical standards of the institution's responsible committee, in accord with the Helsinki declaration of 1975 (as revised in 1983).
Serum osteocalcin was measured by the same solid-phase "sandwich" IRMA used in our laboratory (Osteo-ELSA; CIS bio international, Gif sur Yvette, France). The first antibody was coated on the ELSA solid phase; the second, radiolabeled with 125I, was used as a tracer. The precision was tested by using four samples at different concentrations (between 32.5 and 88.2 µg/L) 30 times in the same assay (CV = 3.5–4.9%, mean 4.2%) and 15 times in successive assays (CV = 3.7–6.2%, mean 4.9%). The minimum detectable concentration (0.4 µg/L) was obtained by repeating in duplicate 20 times the zero calibrator and calculating 3 SD on average.
The median results are shown in Fig. 1
and interquartile ranges in Table 1
. For children between ages 1 and 11 years, median values were
in narrow intervals. In all healthy children, median osteocalcin
concentrations were 
88.5 µg/L. In girls, serum osteocalcin
decreased significantly (P 0.05) after the 12th year,
reaching the values of healthy adult women at the age of 14. In boys
this happened 2 years later, at 16, and the result decreased
significantly (P 0.001) after the 15th year. P
values are calculated with a statistical nonparametric (Friedman) test
for paired groups.
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Previous studies showed increased serum osteocalcin in diseases with increased bone turnover, e.g., renal osteodystrophy, hyperparathyroidism, hyperthyroidism, and Paget disease (7)(8)(9)(10), and decreased concentrations with low bone turnover, e.g., hypoparathyroidism, hypercalcemia resulting from bone metastasis, and long-term cortisone therapy. The decreased serum osteocalcin during prolonged cortisone therapy reflects a decrease of the osteoblastic activity (11). In primary osteoporosis, such as in the postmenopausal form when the phosphocalcic balance is normal, the assay of serum osteocalcin allows classification of the disease according to regeneration rate (high or low remodeling) (12)(13)(14). In contrast, little information is available on serum osteocalcin in children. Some authors have reported higher values in healthy children than in adults; the increase happens at the age at which puberty usually occurs (15).
The decreases of osteocalcin at ages 12 and 15 in girls and boys,
respectively (Fig. 1
), may reflect the later occurrence of puberty in
boys.
The observed median values for osteocalcin in boys and girls ages 1–12 are two or three times those in healthy adults.
Acknowledgments
We acknowledge Marisa Punzo, Angela Sglavo, and Anna Maria Palmieri for excellent technical assistance in the assay procedure.
References
The following articles in journals at HighWire Press have cited this article:
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  M. Rauchenzauner, A. Schmid, P. Heinz-Erian, K. Kapelari, G. Falkensammer, A. Griesmacher, G. Finkenstedt, and W. Hogler Sex- and Age-Specific Reference Curves for Serum Markers of Bone Turnover in Healthy Children from 2 Months to 18 Years J. Clin. Endocrinol. Metab., February 1, 2007; 92(2): 443 - 449. [Abstract] [Full Text] [PDF]
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 K.-S. Tsai, M.-H. Jang, S. H.-J. Hsu, W.-C. Cheng, and M.-H. Chang Bone Alkaline Phosphatase Isoenzyme and Carboxy-Terminal Propeptide of Type-I Procollagen in Healthy Chinese Girls and Boys Clin. Chem., January 1, 1999; 45(1): 136 - 138. [Full Text] [PDF]
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