Bone mineral density

Bone Mineral Density

Bone mineral density (BMD) is a measurement of the level of minerals in the bones, which indicates bone strength and the risk of fracture. It is a crucial parameter in the diagnosis and management of osteoporosis and other conditions that lead to bone loss.

Measurement

BMD is typically measured using a technique called dual-energy X-ray absorptiometry (DEXA or DXA). This method uses low-dose X-rays to assess bone density, usually at the lumbar spine, hip, and sometimes the forearm. The results are expressed in terms of grams of mineral per square centimeter of bone surface area.

T-score and Z-score

The results of a DEXA scan are often reported as T-scores and Z-scores:

• T-score: Compares the patient's bone density with that of a healthy young adult of the same sex. A T-score of -1.0 or above is considered normal, between -1.0 and -2.5 indicates osteopenia, and -2.5 or lower indicates osteoporosis.
• Z-score: Compares the patient's bone density with that of an average person of the same age, sex, and body size. A Z-score of -2.0 or lower is considered below the expected range for age.

Factors Affecting Bone Mineral Density

Several factors can influence BMD, including:

• Age: BMD typically peaks in the third decade of life and declines thereafter.
• Sex: Women generally have lower BMD than men and experience more rapid bone loss after menopause.
• Genetics: Family history can play a significant role in determining BMD.
• Nutrition: Adequate intake of calcium and vitamin D is essential for maintaining healthy bones.
• Physical activity: Weight-bearing exercises can help maintain or increase BMD.
• Hormonal factors: Conditions such as hypogonadism or hyperthyroidism can affect bone density.

Clinical Significance

Low BMD is a major risk factor for fractures, particularly in the elderly. Fractures can lead to significant morbidity, reduced quality of life, and increased mortality. Therefore, assessing BMD is an important step in evaluating fracture risk and guiding treatment decisions.

Management

Management of low BMD and osteoporosis may include:

• Lifestyle modifications: Increasing physical activity, ensuring adequate nutrition, and avoiding smoking and excessive alcohol consumption.
• Pharmacotherapy: Medications such as bisphosphonates, selective estrogen receptor modulators (SERMs), and denosumab can help increase BMD and reduce fracture risk.
• Monitoring: Regular follow-up with repeat BMD measurements to assess the effectiveness of treatment.

See Also

• Osteoporosis
• Fracture risk assessment tool (FRAX)
• Calcium metabolism

References

• Kanis JA, et al. (2008). "Assessment of osteoporosis at the primary health-care level." World Health Organization.
• National Osteoporosis Foundation. "Clinician's Guide to Prevention and Treatment of Osteoporosis."