Repeating a bone mineral density (BMD) scan up to eight years after an initial scan appears to provide little additional benefit for predicting fractures among older postmenopausal women, says a recent article in an American Medical Association journal titled Archives of Internal Medicine.


BMD, as measured through a method known as dual-energy X-ray absorptiometry, helps physicians predict fractures and has become the preferred method for doing osteoporosis screening, according to background information in the article. Current guidelines recommend screening all women for osteoporosis at age 65 using BMD measurements. Little evidence, however, supports the use of repeat BMD testing for evaluating fracture risk, although such additional tests are performed commonly in clinical practice.


Dr. Teresa A. Hillier, of Kaiser Permanente Northwest/Hawaii, in Portland, and colleagues measured total hip BMD in more than 4,100 older women, with an average age of 72, in a study of osteoporotic fractures between 1989 and 1990 and again an average of eight years later. The researchers calculated the rate of change in BMD and followed the women for an average of five years after the repeat BMD to see which women developed fractures. Participants were contacted by postcard every four months, and fractures were verified through radiology reports and X-ray films.


During the follow-up period, 877 women had a non-traumatic, non-spine fracture, including 275 hip fractures, and 340 women developed a spine fracture. On average, the womens initial BMD measurements were low, compared with those of young women, but not in a range suggesting the onset of osteoporosis. The group lost an average of 0.59 percent of their bone mass per year between examinations.


In each of the four BMD models (initial BMD, repeat BMD, change in BMD between the two examinations, and initial BMD plus change in BMD), BMD was a significant predictor of incident non-spine and hip fracture risk, and was associated with spine fractures in which the diagnosis is made based on vertebral shape, the authors write.


In the study, we did not find any improvement in the overall predictive value in a second measure of BMD, obtained a mean [average] of eight years later, in prediction of hip, spine or overall non-spine fracture risk, they say. In other words, the initial BMD was highly, and similarly, predictive of fracture risk in our population.


Despite these findings, a repeat BMD measurement still might be useful in some women, including those with clinical factors that contribute to rapid bone loss and younger women in early menopause.