- Dual-energy x-ray absorptiometry is the gold standard for bone density measurement.
- Don’t rely on bone densitometry alone to estimate fracture risk; combine it with thorough assessment of history and risk factors. Nonetheless, bone densitometry is vital, and can establish a baseline that is useful for monitoring therapy.
- When interpreting densitometry results, base the diagnosis on the lowest score obtained.
- Over her lifetime, a woman’s risk of hip fracture is greater than her risk of breast, endometrial, and ovarian cancer combined.
That’s where the difficulty begins. Amid a profusion of data, the simple how-to—and when-to—of screening can get lost. But osteoporosis is a potent threat. Over her lifetime, a woman’s risk of hip fracture is greater than her risk of breast, endometrial, and ovarian cancer combined. Since many women are discontinuing hormone replacement therapy in the aftermath of the Women’s Health Initiative, the risk seems likely to increase.
This article describes a sensible screening strategy focusing on 6 common pitfalls. Many observations come directly from the clinical setting—specifically, a practice in reproductive endocrinology with special interest in the health-care needs of maturing women.
Scope of the problem
As the National Osteoporosis Foundation (NOF) observes, osteoporosis is a “silent disease until it is complicated by fragility fractures.”1 It affects people of all ages and races, but is most prevalent among postmenopausal white and Asian women. However, even African-American and Hispanic women face a heightened risk.2-4
One of every 2 white women will experience an osteoporotic fracture.1 In fact, after age 65, the incidence of hip fracture in white women is greater than the incidence of stroke, diabetes, or breast cancer.5
For survivors and their loved ones, the diminished quality of life and loss of independence can be devastating. Not surprisingly, many patients also experience psychological symptoms such as depression.
Vertebral fractures are another dire consequence of osteoporosis, causing back pain, loss of height, kyphosis, and even death.
The economic burden of osteoporosis is no less daunting. In 1995, osteoporotic fractures were the “presumed cause” of 180,000 nursing home admissions, more than 430,000 hospital admissions, and roughly 2.5 million doctor visits.1 Each year these fractures cost about $17 billion in health care—or $40,000 per hip fracture.1
Measuring bone density: The basics
Dual-energy x-ray absorptiometry (DXA) is the gold standard for bone-density measurement. It is recommended by the American Association of Clinical Endocrinologists (AACE), the American College of Obstetricians and Gynecologists (ACOG), and the North American Menopause Society (NAMS). Quantitative computed tomography is also recommended by the AACE.
Quantitative ultrasound, which is gaining in popularity, can yield information on bone structure and elasticity in peripheral locations such as the heel, patella, and tibia. It lacks the ionizing radiation of DXA.
It is important for the clinician to be familiar with all these modalities, though the ultimate selection will vary from patient to patient.
Contraindications to densitometry include pregnancy. While the risk during gestation is negligible, it still exceeds potential benefits.
Limitations. A patient who has undergone recent gastrointestinal studies and nuclear medicine tests should wait at least 72 hours before having a central DXA scan.
Morbid obesity may limit the options, since the weight limit of most central DXA scanners is 250 to 350 lb. Check with the manufacturer for machine limitations and obtain a forearm measurement if necessary.
A family history of osteoporosis, particularly in the patient’s mother or another first-degree relative, is a good predictor of the disease.
Orthopedic instrumentation may interfere with measurement at some sites.7
T and Z scores. Osteoporosis is defined by comparing the patient’s bone density to 2 different populations: her own age group and young adults.
- When bone density is compared to that of her own age group, the result is conveyed as a “Z” score, which represents the number of standard deviations away from the mean.
- When it is compared to the peak bone mass of a “normal” young adult, the result is given as a “T” score—again, the number of standard deviations away from the mean. The World Health Organization (WHO) defines osteoporosis as a T score at or below –2.5 (TABLE 1).