Diagnosis of Osteoporosis

The diagnosis of osteoporosis is made of the basis of a diminished bone mineral density (BMD). The most widely accepted means of measuring BMD is with a special x-ray test known as a DEXA (dual x-ray absorptiometry) scan. The test involves two (dual) x-ray beams with different energy levels. DEXA measures the amount of energy from each beam that is able to pass through the bone. Dense bones tend to block the passage of x-rays, while thin, weakened bones allow x-rays to pass more freely. Measurements are most typically taken in the hip and spine. Most scans take between 10 and 20 minutes, and are painless.

The measurement from the DEXA scan is converted into a score called a T-score. This represents a comparison between the bone mineral density of the woman being scanned and the average bone mineral density of a young, healthy adult. Women with loss of bone mineral density have negative T-scores. A T-score of -1 to -2.5 indicates mild bone loss, or osteopenia. A T-score of less than -2.5 (e.g. -2.8) is diagnostic of osteoporosis.5

Premenopausal women are much more likely than postmenopausal women to have secondary osteoporosis, related to an underlying medical disorder. In these women, additional blood tests may be appropriate.