Bone densitometry

Bone densitometry, also known as bone density scanning or dual-energy X-ray absorptiometry (DXA or DEXA), is a form of medical imaging that measures the density of bones. This technique is crucial in diagnosing and assessing the risk of osteoporosis, a condition characterized by weakened bones that are more prone to fracture. Bone densitometry is a key tool in preventive healthcare, allowing for the early detection of bone loss and the monitoring of bone density over time.

Overview

Bone densitometry works by using a small dose of ionizing radiation to produce images of the inside of the body, typically focusing on the lower spine and hips, to measure bone loss. The DXA machine sends X-ray beams with two different energy levels through the bones being examined. By measuring the absorption of each beam by the bones, it calculates the bone density. The results are compared to the bone density of a healthy young adult (T-score) and an age-matched (Z-score) to determine the risk of fractures and osteoporosis.

Indications

Bone densitometry is recommended for:

• Postmenopausal women and men age 50 and older who have risk factors for osteoporosis.
• Individuals who have experienced a fracture under circumstances that would not typically cause bone breakage.
• Anyone receiving, or planning to receive, long-term steroid therapy.
• Patients with a medical condition associated with bone loss, such as rheumatoid arthritis or certain endocrine disorders.

Procedure

The DXA scan is a quick, non-invasive procedure typically completed within 10 to 30 minutes. It involves the patient lying on a table while the scanner passes over the body. No special preparations are required, although patients are usually advised to avoid taking calcium supplements for at least 24 hours before the test.

Interpretation of Results

The primary result from a DXA scan is the T-score, which compares the patient's bone density with that of a healthy young adult of the same sex. According to the World Health Organization (WHO):

• A T-score of -1.0 or above is considered normal.
• A T-score between -1.0 and -2.5 indicates low bone mass (osteopenia).
• A T-score of -2.5 or below is diagnostic of osteoporosis.

The Z-score is also provided, comparing the patient's bone density to what is expected for someone of the same age, sex, weight, and ethnic or racial origin. A Z-score lower than -2.0 may suggest that factors other than aging are causing abnormal bone loss.

Risks and Limitations

The risks associated with bone densitometry are minimal. The amount of radiation exposure is low, especially when compared to other imaging tests. However, it is not recommended for pregnant women due to the radiation risk to the fetus. Limitations of the test include its inability to predict who will experience a fracture but rather indicates the relative risk.

Prevention and Treatment

Preventive measures for osteoporosis include adequate intake of calcium and vitamin D, regular weight-bearing exercise, and lifestyle changes such as quitting smoking and reducing alcohol consumption. Treatment may involve medications that slow bone loss and increase bone density, along with dietary and lifestyle changes.

See Also

• Osteoporosis
• Radiology
• Endocrinology

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