Markers of Bone Metabolism During Adolescence

Table 3 lists the most common available markers of bone formation and bone resorption. Changes in bone biochemical markers during growth, and especially during adolescence, are more complex to interpret than in adults. In the growing skeleton, and particularly during puberty, all the mechanisms contributing to bone turnover (longitudinal growth, modeling, and remodeling) are accelerated (41). In girls, the peak of bone markers is earlier but lower than in boys, reflecting gender differences in pubertal development. The plasma levels of bone formation markers are highest when the velocity of bone mineral accrual is maximal. Plasma and urinary concentrations of bone resorption markers progressively decrease after the growth spurt, reaching adult levels at the end of pubertal maturation (on average, 15 to 16 years for girls and 17 to 18 years for boys). These changes are an expression of the reduction in resorption rate associated with the reduction and arrest in longitudinal bone growth.

In adolescents affected by chronic rheumatic diseases the evaluation of bone markers requires special caution. Age, sex, pubertal stage, disease activity, and therapy must all be taken into account in order to evaluate the actual bone damage (reduced bone formation or increased bone resorption). As in many chronic diseases, growth can be affected, determining low levels of bone markers. An apparently paradoxical increase in bone markers is observed during the successful treatment of rheumatic diseases: it reflects the acceleration of growth and pubertal maturation. Moreover, the bone turnover changes linked to pubertal maturation overlap with the changes due to the effects on bone of chronic inflammation (increased osteoclastogenesis and bone resorption), and to the effects of therapy, mainly corticosteroids.

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