Biochemical measurements of bone turnover in children and adolescents

Biochemical measurements of bone turnover are helpful in the study of the p athophysiology of skeletal metabolism and growth. However, interpretation o f their results is difficult because they depend on age, pubertal stage, gr owth velocity, mineral accrual, hormonal regulation, nutritional status, ci rcadian variation, day-to-day variation, method of expression of results of urinary markers, specificity for bone tissue, sensitivity and specificity of assays. Three markers of bone formation have been described including th eir bone specificity and age-related changes: osteocalcin, alkaline phospha tase and its skeletal isoenzyme, procollagen I extension peptides. Bone res orption markers (hydroxyproline; deoxypyridinoline; pyridinoline; peptides containing these crosslinks such as N-telopeptide to helix in urine (NTX), C-telopeptide-1 to helix in serum (ICTP) and C-telopeptide-2 in urine and s erum (CTX); tartrate-resistant acid phosphatase; hydroxylysine and its glyc osides) are described with special attention to methodologic issues, mainly ways of expression of their results. Changes of bone turnover during growt h are described during four periods: infancy, prepubertal period, puberty a nd the postpubertal period. Pubertal changes of bone markers are described with special attention to gender differences and hormonal mechanisms of the growth spurt which determine differences related to the pubertal stage. Di sturbances of bone turnover in four conditions are described to illustrate the impact of such diseases on growth and formation of peak bone mass: prem aturity, malnutrition, growth hormone deficiency and corticosteroid-treated bronchial asthma. Available data suggest biochemical markers of bone remod eling may be useful in the clinical investigation of bone turnover in child ren in health and disease. However, their use in everyday clinical practice is not advised at present.