Biochemical markers of bone turnover for the clinical investigation of osteoporosis.

The non-invasive assessment of bone turnover has received increasing attention over the past few years because of the need for sensitive markers in the clinical investigation of osteoporosis. Markers of bone formation include the serum measurement of total and bone-specific alkaline phosphatase, osteocalcin, and type I collagen extension peptides. Assessment of bone resorption can be achieved by measurement of urinary hydroxyproline, urinary excretion of the pyridinium crosslinks (pyridinoline and deoxypyridinoline), and by measurement of plasma tartrate-resistant acid phosphatase activity. For the screening of bone turnover in women at the menopause, and for the assessment of the level of bone turnover in elderly women with vertebral osteoporosis, serum osteocalcin and urinary pyridinoline appear to be the most sensitive markers, so far. Programs combining bone mass measurement and assessment of bone turnover by several markers in women at the time of menopause are being developed in an attempt to improve the assessment of the risk for osteoporosis. Efforts are made to develop more convenient assays and to identify other markers of bone turnover. In future a battery of various specific markers is likely to improve the assessment of the complex and subtle abnormalities of bone metabolism that characterize the various aspects of osteoporosis.