Bone mineral density (BMD) tests are the only way to detect osteoporosis. These tests are painless and noninvasive, and they are very helpful in terms of measuring bone strength. There are a number of tests available: central machines, which measure BMD in the hip, wrist, spine, or total body; and peripheral machines, which measure BMD in the finger, hand, forearm, heel, or shin bone.
The most widely used and best understood BMD test is DEXA (Dual Energy X-ray Absorptiometry). DEXA measures BMD of the spine, hip, or total body. While radiation is used to conduct a DEXA scan, it involves approximately a tenth of the radiation required for a single chest x-ray. To conduct this test, the patient rests on a padded table. A large mechanical arm moves over the body, with a total body scan taking approximately 20 minutes to complete.
Results of BMD tests are usually expressed as "T-scores." A T-score involves a statistical term called "standard deviation," a measurement of how far something is away from what is considered "normal." With respect to BMD testing, "normal" has been defined as the average BMD of healthy, young controls (representing peak bone density). If you are a female undergoing BMD testing, your bone density will be compared to that of a population of young, healthy women; if you are a male undergoing BMD testing, your bone density will be compared to that of young, healthy men. A T-score is the number of standard deviations below (or above) these "normal" cases:
- Normal bone: T-score better than -1.
- Osteopenia: T-score between -1 and -2.5 (discussed in the next section)
- Osteoporosis: T-score less than -2.5
BMD testing will also produce what is known as a "Z-score." This compares the BMD of the person being evaluated with the average BMD of people of the same age and sex. However, when it comes to diagnosing osteoporosis, the T-score is of the most importance.
At the present time, there are competing views on when to screen for bone problems in people with HIV. A 2009 set of recommendations by the Infectious DIseases Society of America (IDSA) suggests screening HIV-positive men and women who are over 50, but only if they have another risk factor, such as a previous fragility fracture or the use of medications known to cause bone loss. A more recently published set of recommendations suggests that all HIV-positive men and women aged 50 and older should receive bone scans.
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