This week in the New England Journal of Medicine (1) a report was published looking at the rate of transition to osteoporosis in post menopausal women. Despite the frequency of vertebral and hip fractures in elderly women, and the notable awareness of prevention of osteoporosis, there are, surprisingly, no guidelines for frequency of routine bone density testing in post-menopausal women (except those made by the manufacturers of the equipment and testing facilities who, of course, have a vested interest in very frequent intervals of testing). Medicare will pay for bone densitometry (dual-energy x-ray absorptiomentry, or DXA scanning) every 2 years, and many practitioners recommend screening every 5 years after menopause, and every 2 years if there are any predisposing causes (including previous fracture, smoking, use of corticosteroids, rheumatoid arthritis, cessation of estrogen use, low BMI). The Osteoporotic Fractures Research Group studied 4957 women (99% Caucasian) who underwent DXA scanning at age 65 or older, then repeat DXA scans year 2, 6, 8, 10 and 16. None of the women had bone density measurements at the initial scan that indicated a diagnosis of osteoporosis. The endpoint of interest was transition from non-osteoporosis to osteoporosis. The conclusions seem to support the recurring theme that most normal, healthy people are undergoing routine screening procedures more frequently than necessary.
At the initial scan, the women were divided into 4 groups depending on bone density measurements. Measurements of bone density in an individual are compared to the average bone density of young adults at peak bone density, and are referred to as “T scores”. Bone density measurements more than 1 standard deviation below the average peak bone density is designated as a T score of -1 and results in a diagnosis of “osteopenia” or low bone mass, but not yet officially osteoporotic. A bone density 1 standard deviation below average translates to a bone density lower than 84% of the young healthy population. An official diagnosis of osteoporosis is awarded when bone density of a persons hip or spine is less than 2.5 standard deviations below the average, or a T score of -2.5. This translates to a bone density less than 97% of the young healthy population, or the lowest 3%. The women in the study were divided into a group with normal bone density (T score 0 to1.0), mild osteopenia (T score -1.01 to -1.49) moderate osteopenia (T score -1.5 to -1.99) or severe osteopenia (T score -2.0 to -2.5). The researchers then calculated how long it took for 10% of the women in each group to transition to an official diagnosis of osteoporosis. When a DXA scan is performed, bone density is routinely measured in the spine and the femoral neck, and a T score is assigned to each anatomic area. For this study, the researchers used the lowest T score as the initial measurement and all subsequent measurements.
The results showed that it took more than 15 years for 10% of the women in the group with normal or mildly osteopenic DXA scores to become osteoporotic. It took 4.7 years for 10% of the women with moderate osteopenia to become osteoporotic, and 1.1 years for 10% of the severely osteopenic women to become osteoporotic.
All the women in the study were Caucasian, but frequency of osteoporosis in white women is the same or greater than non–white women, so these results probably are a good estimate of the population as a whole. If the groups were divided up further by age, the elder subpopulations transitioned to osteoporosis faster than the younger subpopulations. For example, in women with moderate osteopenia (T scores -1.5 to -1.99 at the initial DXA scan), the time until 10% developed osteoporosis was approximately 5 years for women who were 70 and approximately 3 years for those who were 85 years old. Another notable aspect of this study is that the initial measurements were taken after age 65. One would expect even longer intervals until transition to osteoporosis in younger women.
The conclusions of this study is that you could expect only a small number of women with T scores greater than -1.5 at age 65 to become osteoporotic over the next 15 years. It therefore seems excessive and wasteful to recommend routine screening every 2-5 years in this group of women. Using the information in this study coupled with the individuals family history and specific risk factors, recommendations for frequency of routine DXA scanning in post menopausal women should be tailored to the individual and not prescribed as a generic blanket recommendation.
1. Gourlay, M.L., Fine, J.P., Preisser, J.S et al. Bone-Density Testing Interval and Transition to Osteoporosis in Older Women. New Eng J Med. 366: 225-33. 2012.
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