Bone density

A bone density test may detect osteoporosis or osteopenia. which is more likely to result in unnecessary treatment rather than discovery of a weakness. • individuals receiving, or planning to receive, long-term glucocorticoid (steroid) therapy. Average bone mineral density = BMC / W [g/cm2] • BMC = bone mineral content = g/cm • W = width at the scanned line Interpretation Results are generally scored by two measures, the T-score and the Z-score. Scores indicate the amount one's bone mineral density varies from the mean. Negative scores indicate lower bone density, and positive scores indicate higher. Less than 0.5% of patients who underwent DXA-scanning were found to have a T- or Z-score of more than +4.0, often the cause of an unusually high bone mass (HBM) and associated with mild skeletal dysplasia and the inability to float in water. T-score The T-score is the relevant measure when screening for osteoporosis. It is the bone mineral density at the site when compared to the "young normal reference mean". It is a comparison of a patient's bone mineral density to that of a healthy 30-year-old. The US standard is to use data for a 30-year-old of the same sex and ethnicity, but the WHO recommends using data for a 30-year-old white female for everyone. Values for 30-year-olds are used in post-menopausal women and men over age 50 because they better predict the risk of future fracture. The criteria of the World Health Organization are: • Normal is a T-score of −1.0 or higher • Osteopenia is defined as between −1.0 and −2.5 • Osteoporosis is defined as −2.5 or lower, meaning a bone density that is two and a half standard deviations below the mean of a 30-year-old man/woman. Z-score The Z-score for bone density is the comparison to the "age-matched normal" and is usually used in cases of severe osteoporosis. This is the standard score or number of standard deviations a patient's bone mineral density differs from the average for their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50, and in children and adolescents. It is most useful when the score is less than 2 standard deviations below this normal. In this setting, it is helpful to scrutinize for coexisting illnesses or treatments that may contribute to osteoporosis, such as glucocorticoid therapy, hyperparathyroidism, or alcoholism. == Prevention ==

To prevent low bone density it is recommended to have sufficient calcium and vitamin D. Sufficient calcium is defined as 1,000 mg per day, increasing to 1,200 mg for women above 50 and men above 70. Other therapies, such as estrogens (e.g., estradiol, conjugated estrogens), selective estrogen receptor modulators (e.g., raloxifene, bazedoxifene), and bisphosphonates (e.g., alendronic acid, risedronic acid), can also be used to improve or maintain bone density. Tobacco use and excessive alcohol consumption have detrimental effects on bone density. Excessive alcohol consumption is defined as more than one standard-sized alcoholic beverage per day for women, and drinking two or more alcoholic beverages per day for men. == Genetics ==

Bone mineral density is highly variable between individuals. While there are many environmental factors that affect bone mineral density, genetic factors play the largest role. Bone mineral density variation has been estimated to have 0.6–0.8 heritability factor, meaning that 60–80% of its variation is inherited from parents. Because of the heritability of bone mineral density, family history of fractures is considered as a risk factor for osteoporosis. ==References==