Markers of bone and collagen metabolism-problems and perspectives in paediatrics

This paper gives a short overview of the physiology of biochemical indices of bone metabolism, their origins, the problems of interpretation of their activities and the most important clinical applications in childhood and adolescence. Markers of bone formation are all osteoblast products that enter the circulation; alkaline phosphatase (bone isoform), osteocalcin and type I procollagen peptides. Most of the traditional and new markers for bone resorption analyse the matrix (collagen) degradation products in urine from osteoclast activity. These include urinary hydroxyproline, hydroxylysine glycosides, total or free pyridinoline cross-links and cross-linked N- or C-telopeptides. Many studies have shown that both the old and new markers of bone metabolism are useful tools for basic bone biology research, for defining physiological phenomena in clinical studies, or drug trials of growth modifying therapies (e.g. growth hormone), and for following up individual patients. For the exact interpretation of bone markers it is necessary to define the factors which may influence measurement of the markers, such as age, sex, puberty, height velocity, circadian rhythms, diet, liver function and kidney clearance rates.