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?
What is a reasonable course?
She has 6 risk factors for bone loss and osteoporosis: estrogen deficiency, current smoking, probable family history, thinness, sedentary lifestyle, and probable calcium deficiency. Every attempt to modify the risk factors that can be modified is worth the effort—smoking cessation, exercise, and calcium and vitamin D supplementation would benefit her skeleton.
Important: Test again in 1 year. It is extremely important to repeat bone density testing at the lumbar spine in 1 year. If the nonpharmacologic interventions you recommend prove insufficient to radically slow the anticipated bone loss, she will fall below a T-score of -1.5 in the next year.
On the other hand, if she demonstrates that she can maintain her bone density with nonpharmacologic measures, a prescription may not be warranted. It would not be unreasonable to allow her this 1 year, because at her relatively young age of 54, at this bone density, her short-term risk of fracture is actually quite low.
“Yes” to both questions
If bone density is low—particularly if it is low and a woman has risk factors for osteoporosis—pharmacologic intervention can be reasonably expected to prevent the devastating consequences of osteoporosis. The question, “Does this menopausal woman need pharmacologic intervention to prevent or treat osteoporosis now, or might she need it later?” can be answered by measuring bone density. It is a question we would be remiss not to ask. Bone density measurement, preferably at the PA lumbar spine and proximal femur by DXA, is the only way to answer this all-important question. To provide the best care possible for a woman who has just become menopausal, you do need to know her bone density. The simple answer to both original questions then, is yes.
Techniques and sites
Bone densitometry can be performed using any of several techniques: dual energy x-ray absorptiometry (DXA), quantitative computerized tomography (QCT), radiographic absorptiometry (RA), or quantitative ultrasound (QUS).
Similarly, bone densitometry can be performed at a myriad of skeletal sites such as the PA lumbar spine, lateral lumbar spine, proximal femur, forearm, phalanges, calcaneus, and total body.
Guidelines are based on PA lumbar or proximal femur by DXA. It is correct that virtually all sites, measured by any technique, predict an individual’s fracture risk, but guidelines for diagnosis of osteoporosis and pharmacologic intervention to prevent or treat osteoporosis are overwhelmingly based on measurements of the PA lumbar spine or proximal femur by DXA.10-14 This is not because of any inadequacy or inaccuracy of the other technologies at these or other skeletal sites. It is because of the use of the World Health Organization (WHO) criteria for diagnosis of osteoporosis and the reliance upon the T-score in intervention guidelines.
WHO diagnosis based on T-score
| DIAGNOSTIC CATEGORY | T-SCORE CRITERIA |
|---|---|
| Normal | -1 or better |
| Osteopenia (low bone mass) | Between -1 and -2.5 |
| Osteoporosis | -2.5 or poorer |
| Severe osteoporosis | -2.5 or poorer, with a fragility fracture |
In its sentinel 1994 guidelines, the WHO defined osteoporosis as a bone density of 2.5 standard deviations (SD) or more below the average bone density for a young adult.15 This threshold was chosen in an attempt to reconcile the prevalence of the disease created by the threshold and the observed lifetime fracture risks. The data used to reach this conclusion were largely based on single-photon absorptiometry (SPA) data from the mid-radius, dual-photon absorptiometry (DXA’s predecessor) and DXA data from the PA lumbar spine and proximal femur.
The WHO warned that applying these criteria in persons measured by other technologies or at other skeletal sites could result in a different diagnostic category. When physicians did apply the criteria in clinical practice, WHO’s prediction became a reality that was quickly recognized and discussed in the literature.
It became clear that we could not apply the WHO criteria to all technologies and all skeletal sites.
Consequentially, major osteoporosis-related medical organizations issued guidelines calling for restricting the diagnosis of osteoporosis based on the WHO criteria to bone density studies performed at the PA lumbar spine and proximal femur using DXA.
T-score means above or below “average”
The T- score on modern bone density reports, although not a technically correct use of the term, indicates your patient’s number of SDs above or below that of the average value for a young adult. If your patient’s BMD is below the average value for a young adult, a minus sign is placed in front of the T- score. The young-adult average value is always assigned a T- score value of 0. For example, a BMD that is 2.2 SD below the average value for a young adult of the same sex would be assigned a T- score of -2.2. Because the WHO defined osteoporosis based on the number of SDs below the average for a young adult, the WHO criteria readily translate to a T- score.
