When To Start Bone Density Testing
Posted by medconsumers on March 1, 2003
“Bone mineral density testing is a poor predictor of future fractures, but an excellent predictor of start of drug use.” Barbara Mintzes, University of British Columbia, British Medical Journal, 4/13/02
The selling of bone density tests to younger women took off, not incidentally, once a fracture-prevention drug became available. In 1997, Merck received approval from the U.S. Food and Drug Administration to promote its new osteoporosis drug Fosamax (alendronate) as a preventive. Initially, Merck’s ads directed to physicians featured a fit-looking woman in her early forties, but now older women are portrayed in the ads directed to the public. (“See how beautiful 60 can look, see how invisible osteoporosis can be?….Ask your doctor if a bone density test if right for you.”)
The change might have been initiated by the 1998 guidelines set by the Osteoporosis Foundation and nine other professional organizations that recommend 65 as the age at which to begin routine bone density measurement. The older age makes sense because there is no point in having your bone density tested unless you are willing to go on drug therapy for years once bone loss is detected. Hip fractures related to bone loss are uncommon before the age of 70; they occur on average at age 79. Moreover, drug therapy is best initiated at an older age because the long-term (more than five years) adverse effects of osteoporosis drugs are unknown.
Fosamax belongs to the only drug class (bisphosphonates) proven to reduce hip fractures. And its efficacy is modest. For example, a major clinical trial that compared Fosamax-treated women for three years showed that 1% (11 women) suffered a hip fracture, as compared to 2% (22 women) taking a placebo, or inert pill.
Another reason for delaying the start of bone density testing was provided last year when the U.S. Preventive Services Task Force announced its new recommendations. Current tests for bone density cannot accurately predict far into the future–that is, identify whether a 55-year-old is likely to fracture at age 79. But the 2002 Task Force report did find that bone density measurement could accurately predict the risk for fractures in the short-term. This is a clear refutation of the screening advice women got in the late 1990s when Merck ads aimed at doctors promoted the idea that screening should begin just before menopause.
Bone density measurement’s poor long-range predictive ability was the central point in a 1998 report from the British Columbia Office of Health Technology Assessment. After a review of the research, the report concluded that a woman could have low bone mass at age 48 and not suffer a hip fracture in old age. Conversely, a woman can have good bone density at age 48 and have a hip fracture at age 79.
The British Columbia report warned, “The greatest concern is that bone density measurement will mislabel most women. More than half of the women who will eventually suffer fractures will be classified as normal.” The U.S. Preventive Services Task Force also concluded that potential harms “may arise from inaccuracies and misinterpretations of bone density tests.” Of the different tests used to measure bone density, the dual-energy X-ray absorptiometry (DXA) was identified as the best at predicting hip fracture.
The Task Force did not find strong or consistent evidence to back up the typical laundry list of risk factors used to encourage women to seek testing. The list includes “white or Asian ethnicity, history of fracture, family history of osteoporotic fracture, history of falls, low levels of physical activity, smoking, excessive alcohol or caffeine use, low calcium or vitamin D intake, and the use of various medications.” Not surprisingly, the strongest risk factor was advanced age and to a lesser degree, a slight build and low body weight (under 150 pounds). Low body weight, however, is enough of a risk factor for the Task Force to recommend that women who fit this description start bone density testing at age 60 years.
Long-term drug therapy is the usual recommendation once severe bone loss has been detected in elderly women and men*. Fosamax and another bisphosphonate called Actonel are the drugs of choice once low bone mass is diagnosed, which is defined as at least 2 standard deviations below the mean for a healthy young woman, or the presence of a fracture.
Estrogen has often been prescribed to women who are diagnosed with osteopenia, which is defined as moderately low bone mass, or one standard deviation below the norm for a healthy young woman. Another drug often prescribed for osteoporosis prevention is Evista. No head-to-head comparison, however, has ever been done with these drugs and the bisphosphonates.
Estrogen clearly preserves bone density, but, unfortunately, the first trial to prove that it could also reduce the rate of hip fractures also showed that the risks far outweighed this benefit. The Women’s Health Initiative trial, which made headlines last summer, found a higher rate of breast cancer, heart attacks, clots, and strokes among women who took estrogen in combination with another hormone progestin. The trial showed no such ill effects for women taking estrogen alone (i.e., those who had had a hysterectomy and did not need progestin); consequently, the Task Force determined that they could delay the start of bone density testing to age 65.
The other osteoporosis drug Evista can increase bone density, but its fracture reduction capabilities are confined to the spine. All trials combined showed that nearly 2% of the Evista-treated women had painful vertebral fractures, as compared with 3% in the placebo group. As noted, only the bisphosphonate drugs have been shown to reduce fractures of the hip which are the most likely to cause disability and death. No osteoporosis drug has been proven to reduce the rate of death.
For More Information
For summary of the scientific evidence from the U.S. Preventive Services Task Force, visit its Web site (www.preventiveservices.ahrq.gov) or call AHRQ Publications Clearinghouse at 1(800) 358-9295.
*Men are usually at a more advanced age than women once severe osteoporosis is diagnosed. And many have drug-induced bone loss from the standard drug therapy for prostate cancer. The clinical trials proving that Fosamax can reduce the rate of hip fracture did not have male participants.
Maryann Napoli, Center for Medical Consumers(c)