The last decade has witnessed important technological advances in the diagnosis of osteoporosis and an increase in therapeutic options. However, there is still considerable uncertainty about optimal strategies for screening and primary preventive treatment.
In 1994, a World Health Organization working group proposed that the diagnosis of osteoporosis be made when BMD, assessed by a dual-energy x-ray absorptiometry (DXA), is at least 2.5 standard deviations below the mean for young adult women (T-score) at the spine, hip, or wrist, or when a history of a traumatic fracture is present.2 A T-score between −1 and −2.5 is designated as osteopenia.
Osteoporosis is defined as “a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture.”1 While no accurate overall measurement of bone strength exists, bone mineral density (BMD) is frequently used as a proxy.
These facts underscore the importance of osteoporotic fractures:
- Only one third of patients regain their prior level of functioning after hip fracture, and one third are discharged to nursing homes.3
- About 1 in 5 patients dies within a year after a hip fracture.
- Vertebral fracture may result in chronic back pain and disability.4
- Existence of fracture greatly increases risk of subsequent fracture.5
- Direct medical costs for osteoporotic fractures are estimated at $13.8 billion in 1995 dollars.6
Prevalence of osteoporosis and fractures
Of American women over age 50 of all races, an estimated 15%, or 5 million, have osteoporosis (based on DXA T-score at the femoral neck) and an additional 40%, or 14 million, have osteopenia.7 In African Americans, the prevalence is about half that of whites.8 The prevalence of osteoporosis assessed by BMD testing increases with age—from 4% of white women aged 50 to 59 to 48% of women aged 80 to 89.9
At least 1 vertebral fracture, as indicated by radiographic criteria, has occurred in 5% of white women aged 50 to 59, and in 25% at age 80.3 The lifetime risk of hip fracture for 50-year-old white women and men is 14% and 5%, respectively; for African American women and men, 6% and 3%, respectively.3 Hip and symptomatic vertebral fractures occur mainly in women over 75,3,10 and the risk for wrist fractures increases starting in the late 50s.11
Age is a particularly important risk factor for hip fractures, reflecting deterioration in bone strength beyond that detectable with BMD testing. The National Osteoporosis Foundation12 observed that the 5-year risk of hip fracture for women with the same T-score (−3) increases dramatically with advancing age (Figure): from 2.4% at age 50 to 9.7% at age 90, with the steepest increase occurring during the 10 years between ages 70 (5.5%) and 80 (9%).
Five-year risk for hip fracture for women with T-score of −3 by age12
Bone mineral density testing
The clinical value of different screening strategies is not established, although recommendations have been made within guidelines and consensus statements that discuss prevention and treatment of osteoporosis. Guidelines are consistent in recommending that BMD screening be done only if results will influence treatment decisions. The US Preventive Services Task Force,13 The National Osteoporosis Foundation,14 and American Association of Clinical Endocrinologists15 recommend screening all women over 65, as well as younger women with risk factors for osteoporosis. The National Institutes of Health3 and the North American Menopause Society16 recommend an individualized decision-making approach to screening. The National Osteoporosis Foundation developed nomograms that integrate risk factors into decision-making for testing and treatment,12 which seem promising and merit testing in prospective studies.
DXA. Although several technologies are available, DXA of the hip is considered the best predictor of hip fracture and an equivalent predictor of other fractures.10 The likelihood of making a diagnosis of osteoporosis based on BMD, however, varies and is related to type of test, equipment, anatomic site tested, number of sites tested, technique, and relevance of the reference range to the local population. For example, when the same group of people is tested with DXA equipment from different manufacturers, the proportion diagnosed with osteoporosis varies by as much as 15%.11
Quantitative ultrasound (QUS) and radiographic absorptiometry (RA). Testing by QUS of the heel and RA of the hand are less expensive than DXA and have become popular. While QUS of the heel has been shown to predict hip fracture and all nonvertebral fractures nearly as well as DXA,3,10 it does not highly correlate with DXA and appears to reflect other aspects of bone quality.10 Since QUS and DXA results frequently disagree and can cause confusion, DXA is the most appropriate test of BMD at present. If QUS and RA are used for screening, confirmation with DXA is recommended before therapy is initiated.