Bone density tests aim to determine whether a woman has or is at risk of osteoporosis. The most common bone density test is a DXA scan that measures bone mineral density compared to the average 30-year-old woman. A loss of bone density increases the risk of bone fracture. Early diagnosis and treatment can prevent further loss and sometimes restore bone density.
Osteoporosis Basics
Osteoporosis is characterized by the gradual loss of minerals, causing bones to weaken and fracture. Although some bone density loss is normal, in osteoporosis the abnormal loss of bone density puts one at risk of fracture. Often a woman is unaware of bone loss until there is a fracture. By then the weakened condition of her bones makes interventions more difficult.
Of special concern are fractures of the hip or spine because of the serious incapacity that can result. Hip fractures always require hospitalization and hip replacement surgery has a better prognosis if the surrounding bones are healthy. Spinal fractures cause severe back pain, a loss of height, and impair mobility.
Bone Density Tests
All bone density tests measure bone mineral density, or BMD. The most commonly used test is a dual-energy X-ray absorptiometry, or DXA test.
A BMD test measures how many grams of calcium and other minerals are in a bone and compares it to the bone density of the average 30-year-old woman, which is when women's bone density is the greatest. BMD tests fairly accurately predict the risk of fracture.
Although any bones can be scanned, the National Osteoporosis Foundation, or NOF, as well as the World Health Organization and the NIH, recommend a BMD test of the hip and spine by a central DXA machine.
How Is It Done?
BMD tests are non-invasive and a person remains fully dressed. They are similar to a usual X-ray and more comfortable than a mammogram. The test usually takes less than 15 minutes.
Although initial BMD results are measured against a standard score, subsequent BMD tests will be compared to your first one to assess additional BMD loss. The most accurate comparisons are when you go to the same place for subsequent BMD tests.
Bone Density Results
Bone density results are measured by T-scores, or standard deviations, which measure how far above or below your bone density is compared to the standard 30-year-old woman. According to World Health Organization definitions:
A T-score between +1 and -1 is normal bone density.
A T-score between -1 and -2.5 indicates low bone density or osteopenia.
A T-score of -2.5 or lower is a diagnosis of osteoporosis.
Who Should Be Tested?
Testing guidelines vary. The NIH cites U.S. Preventive Services Task Force recommendations that women age 65 and older be screened routinely and screening begin at age 60 for women at increased risk for osteoporotic fractures. Other factors may include those taking certain medications, a family history, or early onset menopause. Although the optimal interval for testing is unknown, some organizations suggest two years.
