Osteoporosis for the home care physician. Part 1: etiology and current diagnostic strategies.
Osteoporosis affects over 20 million individuals in North America and is responsible for over 1.5 million fractures in the US. Although most cases of osteoporosis are primary, in 20% of older women and 40% of older men presenting with vertebral fractures, a secondary cause can be identified. The WHO based the diagnosis of postmenopausal osteoporosis on the presence of BMD T-score that is 2.5 standard deviations or greater below the mean for young women. The International Society of Clinical Densitometry defined male osteoporosis as BMD T-score of 2.5 or greater below the mean for young men. BMD assessment at the hip and spine by DXA is the standard procedure to assess bone density. Laboratory testing in patients with low BMD is performed to exclude other conditions that could cause low BMD such as multiple myeloma, endocrinopathies and osteomalacia. Bone turnover marker levels currently do not predict bone mass or fracture risk and are only weakly associated with changes in bone mass. Subsequently, they are of limited use in the clinical evaluation of bone density changes.