I had an X-ray of my hip after a horseback riding accident. According to the radiologist's report, there was no sign of osteoporosis. My neighbor had a different test called "DEXA scanning" that showed she did have early thinning of bone. What is the best test for this problem?

Bone mineral density is a measurement of the mineral content of bone for an area of the body. There are several ways to obtain bone mineral density. There is dual energy X-ray absorptiometry (DXA or DEXA), which measures spine, hip, or total body density. There is peripheral dual energy X-ray absorptiometry (pDXA). This measures wrist, heel, or finger density only. Quantitative ultrasound (QUS) uses sound waves to measure heel, shin, or kneecap density. Other tests include computed tomography (CT) or radiographic absorptiometry (RA), an X-ray of the hand.

These methods do not provide the same information. The DEXA is the best test because it measures bone density at the hip and spine. This is where bone loss occurs most rapidly.

Researchers have measured the bone densities of thousands of women. The peak bone density of women in their 30s is used as a reference point for average bone mass. Osteoporosis is defined as how far a woman's score is from the average peak bone mass. This is called a T-score. A Z-score may also be reported. This is a slightly different measure based on the average bone mass for a woman's age and ethnicity.

T-scores are not the only measure of fracture risk. The whole picture must be considered. For example, a 70-year-old woman with a low T-score is at greater risk of fracture than a 50-year-old woman with the same T-score. This is because other factors increase fracture risk for older people. These include poor eyesight, reduced muscle mass, balance problems, and medications.