• A number of other body composition techniques are available to the clinician. Many of these have their own advantages and disadvantages related to cost, accuracy, and other issues.

• Most clinicians are familiar with anthropometry. Measuring skinfold thickness is the most widely-used technique for estimating fat mass. While handy and inexpensive, observer error is high, even in the most highly-trained individuals.1 It is also not efficient at measuring small changes in body composition, which can be very important in the case of HIV infection.

• Dual energy x-ray absorptiometry, commonly known as DEXA, allows the clinician to distinguish between fat and fat-free tissue. Since it is safe and produces highly accurate and reproducible results, DEXA is considered the gold standard of body composition techniques.2 Given the high cost of equipment and its lack of portability, DEXA is limited to the clinical research arena.

• Isotope dilution methods are used to measure total body water and extracellular water. From these values, lean and fat-free mass can then be calculated.3 Although it can be done fairly easily in the field setting, such methods require an IV, blood drawing, and time. These drawbacks, including cost issues, make isotope dilution methods appropriate for research.

• Computed tomography and magnetic resonance imaging may also be used. Multiscan CT provides an accurate representation of total body skeletal muscle mass in patients with AIDS.4 Long scan times and high cost, however, do not allow their widespread use outside of research.

• Finally, total body potassium counting uses various devices designed to measure the radioactive decay of naturally-occurring 40K, which is considered in direct proportion to the total amount of potassium. Since potassium is absent from adipose tissue, its measurement allows for a highly-accurate way to calculate lean body mass. Although ideal for research purposes, it is too cumbersome for the clinical setting.3

References:

1. Lohman TG. Anthropometric assessment of fat-free body mass. In: Lohman TG, ed: Anthropometric Assessment of Nutritional Status. New York, NY: Wiley-Liss; 1991: 173-83.

2. Heymsfield SB, Wang ZM. Measurement of total-body fat by underwater weighing: new insights and uses for old method. Nutrition. 1993;9:472-3.

3. Koch J. The role of body composition measurements in wasting syndromes. Semin Oncol. 1998;25:12-9.

4. Wang Z, Visser M, Ma R et al. Skeletal muscle mass: evaluation of neutron activation and dual-energy X-ray absorptiometry methods. J Applied Physiol. 1996;80:824-31.