Bone Mineral Density: Clinical Relevance and Quantitative Assessment

Abstract

Bone mineral density (BMD) measurement by dual-energy x-ray absorptiometry (DXA) is an internationally accepted standard-of-care screening tool used to assess fragility-fracture risk. Society guidelines have recommended which populations may benefit from DXA screening and the use of the fracture risk assessment tool (FRAX) to guide decisions regarding pharmacologic treatment for osteoporosis. According to the U.S. National Osteoporosis Foundation guidelines, postmenopausal women and men at least 50 y old with osteopenic BMD warrant pharmacologic treatment if they have a FRAX-calculated 10-y probability of at least 3% for hip fracture or at least 20% for major osteoporotic fracture. Patients with osteoporosis defined by a clinical event, namely a fragility fracture, or with an osteoporotic BMD should also be treated. Patients who are treated for osteoporosis should be monitored regularly to track expected gains in BMD by serial DXA scans. With some drug therapies, BMD targets can be reached whereby further improvements in BMD are not associated with further reductions in fracture risk. Although reaching this target might suggest a stopping point for therapy, the reversibility of most treatments for osteoporosis, except for the bisphosphonates, has dampened enthusiasm for this approach. In the case of denosumab, it is now apparent that stopping therapy at any point can lead to an increase in multiple-fracture risk. For patients who do not respond to antiosteoporosis pharmacologic therapy with an improvement in BMD, or who have an incident fragility fracture on therapy, secondary causes of osteoporosis or non-compliance with medical therapy should be considered.