Bone density tests can help determine if a person is at a risk of developing osteoporosis, a condition in which the bones become porous and susceptible to fractures. This HealthHearty write-up provides information that will help you understand bone density test results.
| According to the Centers for Disease Control and Prevention, more than 4.5 million women aged 50 and above are affected by osteoporosis of the hip in the United States. |
Bone resorption and bone formation are integral aspects of bone remodeling process. Osteoblasts and osteoclasts are specialized cells that are involved in the formation of new bones and resorption of old bones respectively. Though slight loss of bone density is normal with aging, problems are bound to arise if bone resorption takes place at a faster rate, in comparison to bone formation. Bones that have high mineral content are denser and less susceptible to fractures. The risk of osteoporosis increases with the decrease in bone density. Family history, small bone structure, menopause, and fractures after the age of 50 are some of the risk factors for osteoporosis.
Bone density tests are often recommended for people who come under the high-risk group for osteoporosis. Bone scans also can help determine if a person is affected by osteopenia (a medical condition that is characterized by bone loss that is less severe in comparison to osteoporosis) or may develop osteoporosis in the future. Besides their use as a screening test for osteoporosis risk, bone density scans can also help ascertain if a person should take measures to improve bone strength.
| Bone Density Tests |
| Age-related loss of minerals, mass, and structure often puts the affected individuals at a risk of fractures. In people affected by osteoporosis, the spine, hip, and/or the wrist are the most common sites of fractures. Bone density tests can measure the density or the level of minerals in these bones.
The most widely used technique for measuring bone density is DEXA (Dual Energy X-ray Absorptiometry). This test is also called central scan. It is used for measuring bone density in the lower spine and the hip. Peripheral DEXA scans involve the use of small machines to measure the bone density in the forearm and the heel. These scans use a low radiation dose. It must be noted that bone mineral density (BMD) tests can only predict the risk, and cannot be used for predicting the incidence of fractures with certainty. |
| T-score |
| To be able to comprehend the bone density test results, you need to have an understanding of the T-score and Z-score.
T-score is a measure of the density of a person’s bone in comparison to the optimal peak bone density of a healthy 30-year-old adult. The difference between the reference range of healthy young adults with average bone density and the patient’s bone density is calculated and expressed in terms of standard deviations (SD). SD refers to a quantity that is calculated to indicate the extent of deviation. Here’s the interpretation of the T-score as per the World Health Organization: ➞ T-score of -1 or more is indicative of normal bone density. This implies that bone density is normal when the T-score within 1 standard deviation (+1 or -1) of the normal value in a healthy young adult. |
| Z-score |
| Z-score is the measure of the density of a person’s bone in comparison to what’s expected in a person of equivalent age, sex, and size. The Z-score is the number of standard deviations away from the average value of the reference group. It must be noted that the T-score can predict fracture risk better than the Z-score. If your Z-score is -2 or lower, it may suggest that something other than aging is responsible for causing abnormal bone loss.
The T-score is not used for the diagnosis of osteoporosis in case of premenopausal women, men less than 50 years of age, and children. The International Society for Clinical Densitometry (ISCD) recommends that ethnic or race-adjusted Z-scores should be used in such cases. Z-scores of -2.0 or lower are defined as either ‘low bone mineral density for chronological age’ or ‘below the expected range for age’, and those above 2.0 are ‘within the expected range for age.’ The T-score and Z-score can help the doctors determine: ➞ If the patient has osteopenia or osteoporosis prior to fractures, or may develop these conditions after a fracture In case of people diagnosed with osteoporosis, these scores can help the doctors determine: ➞ If the patient’s bone density is constant, improving, or worsening |
People whose T-score is in the osteoporosis range are five times more likely to have osteoporotic fractures. However, the scores only indicate a risk, and there are cases wherein a person with a low bone density may never have a fracture. Moreover, the presence of other risk factors must also be taken into account. As per the National Osteoporosis Foundation (NOF), most osteoporosis-related fractures occur due to falls. Age, anxiety, dehydration, depression, malnutrition, female gender, poor balance, prior fractures, low body mass index, prolonged use of oral glucocorticoids, etc., are some of the risk factors for falls. Thus, decisions regarding the treatment options must not be made on the basis of bone density alone.
