Does menopause always justify bone density testing?
Anne has new-onset hot flashes, Beth’s mother broke a hip, Carol thinks she’s not at risk, Donna has 6 risk factors. Is bone density testing appropriate?
Three guidelines (TABLE)12-14 recommend pharmacologic intervention if the T-score is -2.5 or lower, and these guidelines differ only in the intervention threshold that also requires an additional risk factor. Note that all 3 recommend pharmacologic intervention when there is only a single risk factor in addition to a bone density level that would not be considered osteoporotic by WHO criteria.
The Food and Drug Administration (FDA) has approved drugs for prevention or treatment of postmenopausal osteoporosis, or both, based on whether data demonstrate that a drug:
- inhibits or stops bone loss, for the prevention indication, or
- reduces fracture risk, for the treatment indication.
The FDA-approved dosages of nonestrogen agents may vary by indication (TABLE). In clinical practice, however, the distinction between prevention and treatment is often less clear, leaving the dosage to the judgment of the clinician.
The complete list of clinical risk factors to consider in initiating therapy based on the T-score is lengthy; furthermore, an ever-increasing number of medications and diseases are now known to contribute to bone loss. The 5 major risk factors listed in the margin below are some of the most important to consider along with the T-score.
TABLE
Drug intervention is appropriate when there are…
| NO RISK FACTORS AND A T-SCORE: | RISK FACTORS AND A T-SCORE: | |
|---|---|---|
| National Osteoporosis Foundation | Below -2.0 | Below -1.5 |
| American Association of Clinical Endocrinologists | At or below -2.5 | -1.5 or poorer |
| North American Menopause Society | Below -2.5 | -2.0 or poorer |
| FDA-approved agents for prevention and treatment of postmenopausal osteoporosis* | ||
| Alendronate | ||
| Prevention | 5 mg po qd or 35 mg po qw | |
| Treatment | 10 mg po qd or 70 mg po qw | |
| Ibandronate† | 2.5 mg po qd | |
| Risedronate | 5 mg po qd or 35 mg po qw | |
| Raloxifene | 60 mg po qd | |
| *Unless otherwise noted, doses are the same for prevention or treatment | ||
| †Although FDA-approved, ibandronate is not currently marketed in the United States | ||
Follow-up testing intervals
Once your patient begins drug therapy, it is appropriate to follow up periodically with bone densitometry. The skeletal site measured at follow-up and the intervals between are dictated by reimbursement, as well as scientific issues. Many insurers, including Medicare, reimburse only once every 2 years.16 Exceptions are few.
From a scientific standpoint, BMD increases at the PA lumbar spine may be sufficiently great to be detected in only 1 year, with potent agents like the bisphosphonates or teriparatide. Since changes in PA lumbar spine density are generally less with raloxifene or salmon calcitonin, waiting 2 years to remeasure the PA lumbar spine is entirely appropriate here.
The PA lumbar spine is the preferred site for monitoring therapy because its higher percentage of trabecular bone generally results in a greater magnitude of change than at the proximal femur.
However, the slower rate of change at the proximal femur means that it need not be measured more often than 2 or even 3 years.
If your patient’s bone density is above the pharmacologic intervention threshold, it is always appropriate to counsel her on nonpharmacologic measures to preserve her skeleton: adequate dietary or supplemental calcium and vitamin D, regular weight-bearing or resistance exercise, and avoidance of cigarette smoke.
But we cannot assume that these are sufficient to protect her skeleton. Follow-up bone density studies are recommended to identify women who will lose bone despite these measures, and for whom pharmacologic intervention is warranted. AACE and the North American Menopause Society (NAMS) recommend follow-up bone density studies every 3 to 5 years in postmenopausal women in whom pharmacologic intervention is not deemed immediately necessary.13,14
A more specific approach based on the patient’s lowest T-score at either the PA lumbar spine or femoral neck has been suggested.17 If her T-score is greater than 0, a repeat study is suggested in 5 years. If however, the T-score is 0 to -0.5, a repeat study is suggested in 3 years. A repeat study should be done in only 1 year if the T-score is -0.5 to -1.
This approach assumes that you wish to know when the patient’s T-score might fall below the normal range established by the WHO, that is, below a T-score of -1, and assumes a rate of bone loss of approximately 0.5 SD (or 0.5 T-score units) per year. If you know you would not intervene until the T-score reaches -1.5 or -2, you can adjust the interval accordingly.
Precision in bone density testing is integral to accurate drug therapy monitoring. When properly performed, dual energy x-ray absorptiometry (DXA) bone density measurements are highly, but not perfectly, reproducible. To reflect actual biologic changes, a measured change i n BMD must have sufficient magnitude.
In general, for measurements at the PA lumbar spine or total hip, a change of 2.77% is needed for 95% confidence. The bone densitometry testing facility should provide the clinician with the exact magnitude of the change necessary for a given level of statistical confidence.18 It is also important to remember that while increases in BMD are desirable and reassuring, no loss of BMD may also be considered efficacious.
