Monitoring lipodystrophy

Body-fat changes can be monitored in a number of ways:

• Skin-fold tests: this test uses callipers to measure the quantity of subcutaneous fat. It needs to be done by a dietitian or doctor experienced in use of the test, and can be used to monitor changes in the amount of subcutaneous fat on the arms or legs. However, these changes are not representative of total body fat changes.
• Bioelectrical impedance analysis (BIA): this test passes a small electric current through the body. Since fat is a poor electrical conductor compared to muscle, the body presents an impedance (a more complex measure of electrical resistance) to the current which can be measured and used to determine proportions of overall lean body mass, fat, and other body composition compartments. BIA cannot detect regional changes in body fat, only total body fat changes.
• Dual energy X-ray absorptiometry (DEXA) scan is a method which can show the distribution of fat, muscle and bone in the body, and can detect changes in different parts of the body. It is likely to produce more accurate measurements of fat loss from the limbs, because it cannot distinguish between subcutaneous and visceral fat. However, this test is expensive, requires elaborate equipment which is not available everywhere, and is less accurate in very thin or very obese people.
• Computerised tomography (CT) scan: this is a type of X-ray in which the X-ray source and the scanner rotate around the body. It produces detailed cross-sectional images of the body, and is considered the most accurate measure of whole body subcutaneous and visceral fat. Again, this test is expensive and little used outside of research settings.