How Often Should Healthy Women be Screened for Osteoporosis?

Abstract & Commentary

By Elizabeth Micks, MD, and Alison Edelman, MD, MPH. Dr. Micks is a Fellow in Family Planning, Department of Obstetrics and Gynecology, Oregon Health & Science University; and Dr. Edelman is Associate Professor, Assistant Director of the Family Planning Fellowship, Department of Obstetrics and Gynecology, Oregon Health & Science University, Portland

This article originally appeared in the April issue of OB/GYN Clinical Alert. At that time it was peer reviewed by Catherine Leclair, MD, Associate Professor, Department of OB/GYN, Oregon Health & Science University, Portland, OR. Drs. Leclair, Micks, and Edelman report no financial relationships relevant to this field of study.

Synopsis: In a prospective study of nearly 5000 postmenopausal women, it was determined that it would take 16.8 years to develop osteoporosis in 10% of women with normal bone mineral density. The authors conclude that repeat screening in women without new risk factors can be delayed for at least 15 years.

Source: Gourlay ML, et al. Bone-density testing interval and transition to osteoporosis in older women. N Engl J Med 2012;366:225-233.

In this study, 4957 women aged 67 and older were fol- lowed prospectively for up to 15 years. Statistical models were used to calculate the bone mineral density (BMD) testing interval for women with normal BMD and those with mild, moderate, or advanced osteopenia. The BMD testing interval was defined as the number of years it would take for 10% of women to develop osteoporosis, before having a hip or vertebral fracture and before any treatment for osteoporosis was initiated. For women with normal BMD, the BMD testing interval was determined to be 16.8 years (95% confidence interval [CI] 11.5-24.6). For women with mild osteopenia (T score -1.01 to -1.49), the interval was 17.3 years (95% CI 13.9-21.5). More frequent testing intervals were found for those with moderate (T score -1.5 to -1.99, 4.7 years, 95% CI 4.2-5.2) and advanced (T score -2.0 to -2.49, 1.1 years, 95% CI 1.0-1.3) osteopenia.

Commentary

Osteoporosis, diagnosed by low BMD on dual-energy x-ray absorptiometry (DEXA) scan, is well known to cause significant morbidity and mortality in postmenopausal women.1 BMD accounts for at least three-fourths of the variation in bone strength, and is by far the strongest predictor of fracture risk.2 The American Congress of Obstetricians and Gynecologists (ACOG) and other organizations recommend that all women have DEXA scans starting at age 65, or sooner if they have risk factors for osteoporosis.3 In terms of subsequent screening, however, there has been little evidence for when to recommend the next DEXA scan. The U.S. Preventive Services Task Force4 and ACOG3 currently recommend only that the screening interval should be no more than every 2 years. This important new study provides data on the optimal screening intervals for women with normal BMD, and those with varying degrees of osteopenia.5

To review, The World Health Organization (WHO) uses the T score in its widely used definitions of osteoporosis and osteopenia.6 Osteopenia is diagnosed if hip T score is between -1 and -2.5, meaning between 1 and 2.5 standard deviations below the mean peak BMD in a young adult population. A patient with a T score of < -2.5 has osteoporosis. The main outcome for this particular study was "BMD screening interval," defined as the amount of time it would take for 10% of women to develop osteoporosis after a baseline screening test. The study is not a cost-benefit analysis of DEXA screening for osteoporosis, and the authors don't provide any clear justification for this definition.

The BMD screening interval was found to be 16.8 years for those with normal BMD, and 17.3 years for those with mild osteopenia. Surprisingly, less than 1% of women with normal BMD (T score > -1.00) and 5% of women with mild osteopenia (T score -1.01 to -1.49) actually developed osteoporosis during the 15-year study period. The study found 2.4% of subjects had a hip or vertebral fracture before osteoporosis was diagnosed. Even without critiquing the statistics used by the study authors, we can reassure our patients with normal BMD or mild osteopenia that it is safe to delay repeat screening for much longer than previously thought.

The data were not as reassuring for those with moderate (T score -1.50 to -1.99) or advanced osteopenia (T score -2.00 to -2.49). About 20% of women with moderate osteopenia, and more than 62% of those with advanced osteopenia, developed osteoporosis during the study period. The BMD testing interval for moderate osteopenia was found to be 4.7 years, and just 1.1 years for advanced osteopenia.

Analysis also was performed stratifying by significant clinical risk factors including age, BMI, and baseline estrogen use. Within a specific T-score group, younger women were found to have a longer time interval to osteoporosis. For women with osteopenia, estrogen use during the baseline exam was associated with a longer time interval to osteoporosis. Unfortunately, this did not apply to women who reported prior estrogen use, indicating that the positive effect of estrogen on BMD is not long lasting. For women with advanced osteopenia, higher BMI was associated with a longer time interval to osteoporosis. Other risk factors — including smoking, glucocorticoid use, rheumatoid arthritis, and any fracture after age 50 — were not significant predictors of osteoporosis in this study, even among women with osteopenia at baseline.

When actual fracture risk rather than osteoporosis was examined as the outcome, it was determined that it would take more than 15 years for 2% of women with normal BMD or mild osteopenia to have a femoral or clinical vertebral fracture.

An earlier analysis of the Study of Osteoporotic Fractures (SOF), the same study population as the current publication, in 2007 showed that repeat BMD screening at up to 8 years did not contribute to better prediction of fracture risk beyond the baseline screening.7 To date, these are the only longitudinal studies addressing the optimal frequency of DEXA scans.

For the SOF, 9704 women aged 65 or older in four sites within the United States participated in at least one study examination. From this initial group, 8497 women had adequate baseline BMD data. Of these, about 25% were excluded because they were found to have osteoporosis, and 200 were excluded because they already had a femoral or vertebral fracture or had taken calcitonin. An additional thousand subjects were excluded because they were lacking follow-up data. A total of 4957 subjects were included in the present analysis. Subjects underwent study examinations at year 2, year 6, year 8, year 10, and year 16. Based on T scores, cumulative incidence curves for the time to osteoporosis were developed.

This large prospective, longitudinal study provides much needed evidence for the optimal interval between DEXA scans in women with normal BMD or osteopenia. While we await revised guidelines from ACOG and the U.S. Preventive Services Task Force, we can counsel our patients that osteoporosis develops slowly.

References

1. Gass M, Dawson-Hughes B. Preventing osteoporosis-related fractures: An overview. Am J Med 2006;119(4 Suppl 1):S3-S11.

2. Jergas M, Genant HK. Current methods and recent advances in the diagnosis of osteoporosis. Arthritis Rheum 1993;36:1649-1662.

3. ACOG practice bulletin. Clinical management guidelines for obstetrician-gynecologists. Number 50, January 2004. Obstet Gynecol 2004;103:203-216.

4. Screening for osteoporosis: U.S. preventive services task force recommendation statement. Ann Intern Med 2011;154:356-364.

5. Gourlay ML, et al. Bone-density testing interval and transition to osteoporosis in older women. N Engl J Med 2012;366:225-233.

6. Assessment of fracture risks and its application to screening for postmenopausal osteoporosis. Geneva: World Health Organization;1994.

7. Hillier TA, et al. Evaluating the value of repeat bone mineral density measurement and prediction of fractures in older women: The study of osteoporotic fractures. Arch Intern Med 2007;167:155-160.