Bone strength – material properties of bone tissue, its structural arrangement and amount – can be determined by measuring bone mineral density (BMD). A WHO study group defined osteoporosis by how much it deviates (SD, or standard deviation) from the normal BMD of a healthy young adult. Those with more than 1 SD are diagnosed as having low bone mass, or osteopenia. Those below 2.5 SDs have osteoporosis. If they also have a fragility fracture, they are classified as having severe osteoporosis (WHO, Geneva, 1994).
Ordinary X-rays do not detect bone loss until 25-40% of the bone is a ready lost. The most commonly used technique for measuring bone mineral density is dual-energy X-ray densitometry (DXA), which estimates bone mass at the spine, hip or whole body. Biochemical markers of bone turnover in the blood and urine can provide additional information. Experimental techniques such as ultrasound are being validated and may provide a more cost-effective alternative to BMD measurement as well as supplying additional information relating to bone quality.
Researchers agree on the need for better screening techniques but disagree on optimal timing. Some believe it should be done at the menopause, when women lose bone most rapidly. Others think it is more cost-effective to do it later in life, when fracture risk is highest. Screening is generally recommended for women who decide not to take hormones at the menopause and for others believed to be at risk.
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