Early diagnosis of osteoporosis can prevent fractures and slow deterioration of bone tissue. By measuring bone mineral density (BMD) physicians determine if a patient has osteoporosis and/or is at risk for bone fracture. This testing also helps to monitor the effectiveness of treatment. BMD testing is a quick, noninvasive, and painless procedure.
A person who has had a fracture due to fragility is diagnosed with severe osteoporosis and has a high risk for another fracture. Women and men who are at high risk for osteoporosis, even if asymptomatic, may benefit from BMD testing. Criteria include the following:
- Over age 65, with or without other risk factors
- Postmenopausal and has had a fracture
- Considering therapy for osteoporosis
- Long-term steroid treatment
- Medical condition associated with osteoporosis
In early postmenopausal women, testing focuses on BMD in the spine. In women over 65, bone density in the hip, spine, or wrist can be measured.
Dual-energy x-ray absorptiometry (DEXA) scans the entire body and measures BMD. From the results, physicians assess the risk for fracture in the hip, spine, and wrist. DEXA produces a high resolution image, resulting in a precise BMD measurement. The level of radiation is low and the test takes less than 5 minutes. DEXA effectively monitors changes in bone density during treatment.
Quantitative computed tomography (QCT) measures bone density in the hip and spine and produces a three-dimensional image that shows true volume density. QCT has the capacity to isolate an area for testing. The radiation level in QCT is 10 times higher than in DEXA.
Peripheral bone density testing uses ultrasound to identify bone loss in a localized area such as the heel or hand.
BMD measurement is given as a T-score and a Z-score:
- T-score: the deviation from the mean bone density of healthy young adults of the same gender and ethnicity
- Z-score: the deviation from the mean bone density of adults of the same age and gender
The World Health Organization (WHO) uses a T-score of 2.5 to define osteoporosis. A T-score between -1 and -2.5 indicates some bone loss (osteopenia) and a risk of osteoporosis. Every standard deviation below normal doubles the risk for fracture:
- -1 standard deviation equals 2 times the risk of fracture
- -2 standard deviation equals 4 times the risk of fracture
- -3 standard deviation equals 8 times the risk of fracture
The Z-score is used to classify the type of osteoporosis. A score below 1.5 indicates primary osteoporosis, which is age related. A score of 1.5 and higher indicates secondary osteoporosis, which is associated with calcitonin imbalance, malabsorption conditions (e.g., celiac disease, cystic fibrosis, lactose intolerance), alcohol abuse, smoking, and the use of certain medications.
X-rays can only verify advanced bone loss, vertebral collapse, and bone fractures.