The Importance of Bone Mineral Density Exams (DXA scans)

A dual-energy absorptiometry (DXA) scan can provide a snapshot of your bone
health. This test determines bone mineral density (BMD) and helps in establishing
fracture risk, and, with serial testing, is a way to measure response to osteoporosis
treatment. The most widely recognized test for determining BMD is the central DXA
scan. It is painless – similar to having an x-ray but much less radiation. The scan
measures bone density at your hip and spine. (Often, a scan of the forearm will also
be performed during central DXA testing.) Peripheral bone density testing measures
density at the wrist, finger, or heel and are typically used for screening purposes only.

DXA scans measure your bone mineral density and compares it to that of an 
established norm or standard to give you a score. Although no bone density test
is 100-percent accurate, the central DXA can be an important predictor of 
whether a person will have a fracture in the future. Most commonly, DXA results
are compared to the ideal or peak bone mineral density of a healthy young adult,
and given a T score. A score of 0 means your BMD is equal to the norm for a
healthy young adult. Differences between your BMD and that of a healthy young
adult norm are measured in units called standard deviations (SDs). The more 
standard deviations below 0, indicated as negative numbers, the lower your BMD 
and the higher your risk of fracture.

The National Osteoporosis Foundation (NOF) and the U.S. Preventative Services Task
Force (USPSTF) recommended osteoporosis screening with DXA for women 65 years
and older, and for men over 70. Earlier screening is recommended for both groups if risk
factors are present. (Risk factors are such things as family history of osteoporosis, 
weight under 127 pounds, history of smoking or excessive alcohol consumption, poor
diet, etc.)

A recent review published in the Journal of General Internal Medicine determined that
too few women are getting bone density scans. Researchers examined the medical 
records of 51,000 women aged 40 to 85 living in California and determined that only
57.8% of women aged 65 – 74 and 42.7% of women over age 75 received DXA
screenings. Even with women age 60 to 64 with at least one risk factor, only 58.8%
had a DXA. The researchers concluded that DXA screening is being underutilized.