NEW DEVELOPMENTS IN BIOCHEMICAL MARKERS FOR OSTEOPOROSIS

The noninvasive assessment of bone turnover has markedly improved in t he past few years with the development of sensitive and specific marke rs of bone formation and bone resorption. Markers of bone formation in serum include total and bone-specific alkaline phosphatase, osteocalc in, and type I collagen carboxyterminal extension peptide. Assessment of bone resorption can be achieved by measuring plasma tartrate-resist ant acid phosphate and the urinary excretion (and possibly serum level s) of bone type I collagen degradation products: hydroxyproline, hydro xylysine glycosides, and, more recently, the pyridinium crosslinks (py ridinoline and deoxypyridinoline) and associated peptides. The immunoa ssay of human osteocalcin and bone alkaline phosphatase for formation and the pyridinoline crosslinks measured by high-pressure liquid chrom atography or by immunoassay for bone resorption are currently the most sensitive and specific markers of bone turnover for the clinical asse ssment of osteoporosis. Using these new markers, several studies have shown that bone turnover increases after the menopause and remains ele vated in late postmenopausal and elderly women. An increased bone turn over rate is related to a high rate of bone loss in postmenopausal wom en and to a decreased bone mass in elderly women. Recent data suggest that some of the new immunoassays for pyridinoline crosslinks could pr edict the subsequent risk of hip fracture in elderly women. Thus, bone markers might be used in combination with bone mass measurement to im prove the prognostic assessment of postmenopausal women, i.e., their r isk of developing osteoporosis and ultimately fractures. Treatment of postmenopausal women with antiresorptive drugs such as estrogens, bisp hosphonates, and calcitonin induces a rapid decrease in the levels of bone markers that is correlated with the long-term effect of such trea tments on bone mass. Thus, bone markers should be very useful in monit oring treatment efficacy in patients with osteoporosis.