Bone density measurement--a systematic review. A report from SBU, the Swedish Council on Technology Assessment in Health Care.

Because a reduction in bone density often correlates to an increased risk of fracture, bone density is usually measured in an attempt to establish the risk of fracture. The results from bone density measurement are intended to provide a potential basis for treating osteoporosis. When assessing the value of bone density measurement, the key issues concern the reliability of the various methods (i.e., how accurately they reflect bone density) and whether bone density treatment can actually prevent fracture. OSTEOPOROSIS: Humans begin to lose bone tissue as they become older. In most cases, this process is slow and gradual. Bone tissue begins to disappear when people are aged between 30 and 40 years and continues throughout life. However, bone loss varies greatly among individuals, and some elderly people show no sign of bone loss. Several factors influence both the loss of bone mass as people age and the formation of bone mass in the growing individual. The single most important factor associated with reduced bone mass is the loss of the female sex hormone (oestrogen). Tobacco smoking, lack of exercise, and low calcium levels in the diet also reduce bone density. Reduced bone density may lead to osteoporosis, which increases the risk of fracture, often affecting the vertebrae, hips and wrists. The most common direct cause of fracture, mainly among the elderly, involves falling or stumbling. Contributing factors here include diseases or medications that affect the sight, muscle strength, and balance. Osteoporosis is one of many risk factors for fractures resulting from falls. Fracture is a large and growing health problem. Each year, approximately 60,000 people in Sweden suffer some type of fracture. With an increasing percentage of elderly people in the Swedish population, it is estimated that every second woman over 50 years of age will experience fracture at some time during their remaining life. The risk in men is lower. It is essential to prevent, as far as possible, the onset of osteoporosis and other risk factors for fracture. Preventive approaches include, increased physical activity during youth when people develop their bone mass, sufficient intake of calcium in the diet among the young and old alike, and smoking cessation (or preventing people from starting to smoke). It is particularly important to treat osteoporosis effectively, or prevent osteoporosis from developing into a serious condition. This requires further research into strategies for treating osteoporosis. The various methods for measuring bone density represent an important component in such research. MEASURING BONE DENSITY: Bone density may be measured either to establish a diagnosis or to monitor changes, e.g. follow-up treatment for osteoporosis. Bone density can be estimated roughly by simply measuring height, weight, and age, but this approach has limited value for establishing the level of bone density in individuals. To a certain extent, x-ray examination can also be used to estimate the level of bone density. Special methods have been developed in recent decades for measuring bone density, and technologies for this purpose have become more widely available since the 1980s. The new methods for bone density measurement are based on either the energy/methodology used in ultrasound and magnetic resonance imaging (MRI), or on x-rays. Some methods are designed for measuring only the forearm, hip, lumbar spine, or heel bone (calcaneus), while others measure several sites in the body simultaneously. Most methods demonstrate good precision (i.e. repeated measurements yield the same results). However, to establish the bone density level reliably, methods must also be highly accurate (i.e. the values obtained by measurement must coincide with the individual's actual bone density). The accuracy of current technologies is substantially lower than their precision, so further research, technical development, and experience are required before the methods can be i