Biochemical markers of bone metabolism

Bone metabolic homeostasis is regulated by a number of hormones and local modulators, and the study of these factors has been of major help in our understanding of bone disease. However, these parameters do not, in a strict sense reflect the metabolic and biochemical changes in the diseased bone tissue. Thus, there is a great interest in the study of biochemical specific "markers" of bone metabolic processes, namely of bone formation and bone resorption. Alkaline phosphatase, osteocalcin, osteonectin, and procollagen type I propeptides are the currently known markers of bone formation, whereas urinary hydroxyproline and hydroxylysine glycosides, plasma tartrate resistant acid phosphatase, and urinary hydroxy-pyridinium crosslinks of collagen are considered markers of bone resorption. In this paper, we review the background work on each of these markers, and subsequently give an overview of the currently available data on their usefulness in metabolic bone diseases, namely in Paget's disease of bone, primary hyperparathyroidism, osteoporosis, and renal osteodystrophy.