What is a Bone Density Scan?

A bone density scan is a noninvasive and painless test to evaluate the quality of a person's bones. Also called a dual-energy X-ray absorptiometry (DXA) scan, the test uses X-rays to determine the amount of calcium and other minerals in certain bones of the body. A person with a high mineral content has dense bones. The more dense bones are, the less likely they are to fracture. The scan is often used to determine if a person has osteoporosis and the potential for breaking bones.

The scan is performed using equipment called a central device or peripheral device. A central device is a large machine, often found in medical offices and hospitals, which uses a scanner that passes over an individual while he or she lies still on a long, flat table. The scanner then produces image on a computer. While the scanner does not touch the person, the device does emit radiation, about one-tenth of the amount produced during a chest X-ray. A central device is commonly used to examine the bones in the spine and hip.

Peripheral devices are smaller, portable machines more often found in drugstores or similar locations. The machine is often used to perform a bone density scan of the heel, wrist, or finger. Unlike the central device, the peripheral device requires the individual to place a portion of his or her body into a box-like structure to produce an image.

The bone density scan results are given in two measures, T-scores and Z-scores. These scores indicate how a person's bone density compares with individuals who have similar characteristics. Results are reported in standard deviation, providing an indication if an individual's bone density is higher or lower than average.

A T-score compares an individual's bone density with that of healthy adults of the same gender with similar bone mass. The more negative the number, the weaker a person's bones are. A normal T-score is above -1. A person with a score between the normal and -2.5 is considered at risk for osteoporosis. A score below -2.5 indicates an individual has osteoporosis.

A Z-score represents how a person's results compare with other individuals who are the same age, gender, weight, and ethnicity. In this bone density scan score, a result of -1.5 signifies low bone density. Further testing is often recommended for a person with an abnormal Z-score.

Bone density scans are particularly helpful for elderly men and women. The older one becomes, the higher the risk for osteoporosis, especially in postmenopausal women. Scans are recommended for women 65 or older and for men 70 or older.