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DESCRIPTIONUsing low-dose x-rays of two different energy levels, whole body dual x-ray absorptiometry (DXA) measures lean tissue mass and total and regional body fat, as well as bone density. DXA scans have become a tool for research on body composition (eg, as a more convenient replacement for underwater weighing). This policy addresses potential applications in clinical care rather than research use of the technology.
Measurements of body composition have been used to study how lean body mass and body fat change during health and disease and have provided a research tool to study the metabolic effects of aging, obesity, and various wasting conditions such as occurs with acquired immune deficiency syndrome (AIDS) or post-bariatric surgery. A variety of techniques has been researched, including most commonly, anthropomorphic measures, bioelectrical impedance, and dual x-ray absorptiometry (DXA). All of these techniques are based in part on assumptions regarding the distribution of different body compartments and their density, and all rely on formulas to convert the measured parameter into an estimate of body composition. Therefore, all techniques will introduce variation based on how the underlying assumptions and formulas apply to different populations of subjects (i.e., different age groups, ethnicities, or underlying conditions). Techniques using anthropomorphic, bioelectrical impedance, underwater weighing, and DXA are briefly reviewed as followed.
Anthropomorphic techniques for the estimation of body composition include measurements of skin-fold thickness at various sites, bone dimensions, and limb circumference. These measurements are used in various equations to predict body density and body fat. Due to its ease of use, measurement of skin-fold thickness is one of the most commonly used techniques. The technique is based on the assumption that the subcutaneous adipose layer reflects total body fat, but this association may vary with age and gender.
Bioelectrical impedance is based on the relationship between the volume of the conductor (i.e., the human body), the conductor's length (i.e., height), the components of the conductor (i.e., fat and fat-free mass), and its impedance. Estimates of body composition are based on the assumption that the overall conductivity of the human body is closely related to lean tissue. The impedance value is then combined with anthropomorphic data to give body compartment measures. The technique involves attaching surface electrodes to various locations on the arm and foot. Alternatively, the patient can stand on pad electrodes.
Underwater weighing (UWW) requires the use of a specially constructed tank in which the subject is seated on a suspended chair. The subject is then submerged in the water while exhaling. While valued as a research tool, weighing people underwater is obviously not suitable for routine clinical use. This technique is based on the assumption that the body can be divided into two (2) compartments with constant densities: adipose tissue, with a density of 0.9 g/cm³, and lean body mass (i.e., muscle and bone), with a density of 1.1 g/cm³. One limitation of the underlying assumption is the variability in density between muscle and bone; for example, bone has a higher density than muscle, and bone mineral density varies with age and other conditions. In addition, the density of body fat may vary, depending on the relative components of its constituents (e.g., glycerides, sterols, and glycolipids).
Dual X-Ray Absorptiometry
While the above techniques assume two (2) body compartments, dual x-ray absorptiometry can estimate three (3) body compartments consisting of fat mass, lean body mass, and bone mass. DXA systems use a source that generates x-rays at two (2) energies. The differential attenuation of the two (2) energies is used to estimate the bone mineral content and the soft tissue composition. When two (2) x-ray energies are used, only two (2) tissue compartments can be measured; therefore, soft tissue measurements (i.e., fat and lean body mass) can only be measured in areas where no bone is present. DXA also has the ability to determine body composition in defined regions (i.e., in the arms, legs, and trunk). DXA measurements are based in part on the assumption that the hydration of fat-free mass remains constant at 73%. Hydration, however, can vary from 67%–85%, and can be variable in certain disease states. Other assumptions used to derive body composition estimates are considered proprietary by DXA manufacturers.
Body-composition software for several bone densitometer systems have been approved by the U.S. Food and Drug Administration through the premarket approval process. This includes Lunar iDXA systems (GE Healthcare, Madison, WI), Hologic DXA systems (Hologic, Bedford MA), and Norland DXA systems (Norland, at Swissray, Fort Atkinson, WI).
POLICYDual x-ray absorptiometry (DXA) body composition studies are considered investigational.
POLCIY EXCEPTIONSFederal Employee Program (FEP) may dictate that all devices approved by the U.S. Food and Drug Administration (FDA) may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.
POLICY GUIDELINESInvestigative is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized as a generally accepted standard of good medical practice for the treatment of the condition being treated and; therefore, is not considered medically necessary. For the definition of Investigative, “generally accepted standards of medical practice” means standards that are based on credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community, and physician specialty society recommendations, and the views of medical practitioners practicing in relevant clinical areas and any other relevant factors. In order for equipment, devices, drugs or supplies [i.e, technologies], to be considered not investigative, the technology must have final approval from the appropriate governmental bodies, and scientific evidence must permit conclusions concerning the effect of the technology on health outcomes, and the technology must improve the net health outcome, and the technology must be as beneficial as any established alternative and the improvement must be attainable outside the testing/investigational setting.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY6/16/2008: Policy added
7/17/2008: Reviewed and approved by the Medical Policy Advisory Committee (MPAC)
12/31/2008: Code reference section updated per 2009 CPT/HCPCS revisions
6/23/2010: Policy statement unchanged. FEP verbiage added to Policy Exceptions section. CPT Code 0028T was removed because the code was deleted 12/31/2008. CPT Code 76499 was added to the Non-Covered Codes Table.
04/20/2011: Policy reviewed; no changes.
01/18/2012: Policy reviewed; no changes.
04/01/2013: Policy reviewed; no changes.
03/07/2014: Policy reviewed; no changes.
01/30/2015: Policy reviewed; no changes.
07/23/2015: Code Reference section updated for ICD-10.
01/18/2016: Policy title updated to remove "DEXA." Policy description updated regarding body-composition software. Policy statement updated to change "DEXA" to "DXA." Investigative definition updated in policy guidelines section.
05/31/2016: Policy number added.
SOURCE(S)Blue Cross & Blue Shield Association Policy # 6.01.40
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.