Osteoporosis is a condition in which patients lose some of the mineral in their bones. This decreased bone mass can lead to the bones becoming brittle and fracturing more easily. If caught early, the effects of osteoporosis can be minimized. One way of testing for osteoporosis involves the use of bone density tests.
DEXA Scan
As the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) explains, the first step in getting a bone density test is typically a special kind of X-ray test called a DEXA scan. DEXA stands for dual-energy X-ray absorptiometry and uses low energy X-ray beams to assess the density of the bones.
The DEXA scan measures how much of these X-rays the bones absorb; the denser the bones are, the more of the X-rays they will absorb. There are two kinds of DEXA machines. Portable DEXA machines are often used at pharmacies and health fairs to quickly scan bones in the arms and wrist. Central DEXA scans, however, are usually used in health care settings. These machines require the patient to lie down while the scanner passes over their pelvis and spine. Measurements of the pelvis and spine are generally better indicators of the patient's bone health.
Statistical Tests
Once the results of the DEXA scan have been obtained, the next step is to do some statistical tests on the numbers. Medline explains that the two kinds of statistical analyses that are done on these results are called a T-test and a Z-test. These tests involve comparing the patient's DEXA results to the results from two different healthy populations. The T-test compares the patient's results to healthy young women, whereas the Z-test compares the patient to healthy people of a similar age group. Negative results indicate that the patient has lost some bone density: a T-score of less than -2.5 indicates osteoporosis. Because most people lose bone as they age, the Z-score is considered to be a better indicator of bone health, however, because it helps compensate for some of the natural bone loss.
Bone Scans
Patients with low DEXA scores may need to receive a follow-up bone scan. Bone scans involve injecting the patient with a special dye that is absorbed by the bone and can be detected by a special scanner. This allows doctors to identify recent changes in bone structure and can be used to assess the areas of low bone density, as well as diagnose recent fractures that may have gone undetected.
