A bone mineral density (BMD) test is the best way to determine your bone health. The test can identify osteoporosis, determine your risk for fractures (broken bones).
Bone density is a medical term referring to the amount of mineral matter per square centimeter of bones. Bone density is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk.
A bone density test uses X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone.
The absolute amount of bone as measured by bone mineral density testing generally correlates with bone strength and its ability to bear weight. The BMD is measured with a dual energy X-ray absorptiometry test.
It is measured by a procedure called densitometry performed in the radiology departments. The measurement is painless and non-invasive and involves low radiation exposure.
By measuring BMD, it is possible to predict fracture risk in the same manner that measuring blood pressure can help predict the risk of stroke.
The T-score is the relevant measure when screening for osteoporosis. It is a comparison of a patient's BMD to that of a healthy thirty-year-old.
The Z-Score is the number of standard deviations a patient's BMD differs from the average BMD of their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50 and in children
- Normal : A bone BMD is considered normal if the T-score is within 1 standard deviation of the normal young adult value. T-score between 0 and -1 is considered a normal result.
- Low Bone Mass (Osteopenia) : A BMD defines osteopenia as a T-Score between -1 and -2.5. This indicates an increased fracture risk.
- Osteoporosis : A BMD greater than 2.5 standard deviations from the normal identify osteoporosis.
BMD analysis is recommended for women between ages 50 and 65 with risk factors for osteoporosis and for all women over the age of 65.
Osteoporosis
Osteoporosis is a condition that is characterized by bones that are less dense than normal bone. Osteoporosis increases the risk of breaking a bone with even minor trauma such as a fall from standing height or even from a cough or sneeze.
Osteoporosis is a deconditioned state in which bones become weak and get worse over time. It is a loss of bone mineral density and bone mass which can cause your bones to become fragile and more likely to break.
Bone is constantly being remodeled. This is healthy state of continuous uptake of old bone (resorption) followed by the deposit of new bone.
Bone formation initially exceeds bone resorption, but by the third decade this has reversed resulting in a net loss of bone mass. This leads to an increased bone fragility and susceptibility to fracture.
The cells that lay new bone down are called osteoblasts and the cells responsible for resorption of old bone are called osteoclasts. Osteoporosis occurs as a result of a mismatch between osteoclast and osteoblast activity.
This mismatch can be caused by many disease or hormonal changes. It is also result of aging, change in normal hormones as occurs after menopause and with diets low in calcium and vitamin D.
Women are four times more likely to develop osteoporosis than men. Other risk factors are older age, family history of osteoporosis, thin stature, inactive lifestyle, smoking, alcohol, and use of certain medications including steroids.
The result is a thinning of the bone with an accompanying loss in bone strength and a greater risk of fracture.
Most of a person's bone mass is achieved by early adulthood. After that time, the bone mass gradually declines throughout the rest of a person's life. There is a normal rate of decline in bone mass with age in both men and women.
For women, the menopause transition itself causes an extra degree of bone loss. Women can lose up to 20% of the total bone mass during this time.
Men may also be at risk for osteoporosis if they have certain illnesses, low testosterone level, are smokers, take certain medicines or are inactive. The best method to prevent osteoporosis is to achieve as high a bone mass by early adulthood with a proper diet and regular exercise.
The purpose of BMD testing is to help predict the risk of future fracture so that the treatment program can be optimized.
The following are risk factors for low bone density :
- Rheumatoid Arthritis
- Low Body Weight
- Parent with a Hip Fracture
- Individuals with Vertebral Abnormalities
- Long-Term Glucocorticoid (Steroid) Therapy
- Primary Hyperparathyroidism
- History of Eating Disorders
- Thyroid Disease
- Excessive Caffeine Consumption
Other considerations include smoking habits, drinking habits, the long-term use of corticosteroid drugs, and vitamin D deficiency.
Dual Energy X-Ray Absorptiometry (DXA) is the most common method to measure a patient's BMD. DXA is relatively easy to perform and the amount of radiation exposure is low. At present, DXA scanning gives information on the BMD two main areas, the hip and spine.
Ultrasound is a relatively new diagnostic tool to measure BMD. There is no radiation source with this procedure. An ultrasound beam is directed at the area being analyzed. The scattering and absorption of the waves allow for an assessment of bone density.
