DXA and Osteoporosis

Osteoporosis is characterized by loss of bone mass increased risk of fracture. There is no cure for osteoporosis and a cause has yet to be identified. However experts believe that bone mineral density, or bone mass is the most important factor and single biggest predictor of fracture risk. There are tests available that can measure bone mineral density. Bone density scanning or BMD is an enhanced form of X- ray technology using densitometry.

Dual Energy X-ray Absorptiometry

DXA, DEXA or Dual Energy X-ray Absorptiometry is todays gold standard and most widely used for measuring bone mineral density to diagnose osteoporosis and assess risk for fracture. DEXA is also effective in tracking the effects of treatment for osteoporosis and other conditions that cause bone loss.

There are two types of DEXA equipment. Central devices which measure bone density I the hip and spine, and peripheral devices or pDEXA that measure bone density in more localized areas such as the finger, wrist, kneecap, shin bone and heel.

Central DEXA devices have a large flat table and an arm of sorts suspended overhead. This arm swings away so that the table can be used as an exam chair or treatment table and are usually located in hospitals or larger medical practices.

pDEXA devices are smaller portable structures that can often be found in mobile health vans and even drug stores in the community. They are box like, weighing only about 60 pounds and have a space for the finger, foot, or forearm to be placed for imaging.

Exam Procedure

DXA examinations are done on an outpatient basis. In the central DXA examination a patient lies on a padded table. The x-ray generator is located below the person and a detector, or imaging device is positioned above. To assess the hip a patients foot is placed in a brace that rotates the hip inward, for spine assessment the patients legs are supported by a padded box in order to flatten the pelvis and lower spine.

In either case the detector is slowly passed over the area and generates images on a computer monitor. A pDXA is an even simpler test. The patient’s finger, hand, forearm or foot is placed in a small device that obtains a bone density reading within a few minutes.

A radiologist will analyze the images and send a signed report to the primary care physician who will then share the results. Other types of doctors such as rheumatologists and endocrinologists may also interpret the results. BMD measurement is given as a T score and a Z- score.

The T score is the deviation from the mean bone density of healthy young adults of the same gender and ethnicity. The Z score is the deviation from the mean bone density of adults of the same age and gender. A score above -1 is considered normal. A score between -1 and -2.5 is classified as Osteopenia, the first stage of bone loss. A score below -2.5 is given as a diagnosis of osteoporosis. The T score is used to determine risk of developing a fracture.