Medical Policy: 06.01.31
Original Effective Date: September 2013
Reviewed: April 2016
Revised: April 2016
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This Medical Policy document describes the status of medical technology at the time the document was developed. Since that time, new technology may have emerged or new medical literature may have been published. This Medical Policy will be reviewed regularly and be updated as scientific and medical literature becomes available.
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 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 (ie, different age groups, ethnicities, or underlying conditions). Techniques using anthropomorphics, bioelectrical impedance, underwater weighing, and DXA are briefly reviewed as followed.
Anthropomorphic techniques for the estimation of body composition include measurements of skinfold 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 skinfold 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 sex.
Underwater weighing 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 2 compartments with constant densities: adipose tissue, with a density of 0.9 g/cm3, and lean body mass (ie, 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 (eg, glycerides, sterols, glycolipids).
Whole Body Dual X-Ray Absorptiometry (DXA)
While the cited techniques assume 2 body compartments, DXA can estimate 3 body compartments consisting of fat mass, lean body mass, and bone mass. DXA systems use a source that generates x-rays at 2 energies. The differential attenuation of the 2 energies is used to estimate bone mineral content and the soft tissue composition. When 2 x-ray energies are used, only 2 tissue compartments can be measured; therefore, soft tissue measurements (i.e. fat and lean body mass) can only be measured in areas in which no bone is present. DXA also has the ability to determine body composition in defined regions (i.e. 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% to 85% and can be variable in certain disease states. Other assumptions used to derive body composition estimates are considered proprietary by DXA manufacturers.
The use of DXA in the evaluation of body composition is becoming more widespread. Its purported uses entail determining appropriate nutritional support during disease progression and monitoring response to therapeutic interventions It can be easily used in clinical studies and in various health care delivery locations, as a more convenient replacement for underwater weighing. However, one disadvantage is in regards to follow up. Follow up of a patient requires the use of the same DXA scanner and caution is needed when comparing results from different scanners.
The evidence for DXA body composition studies in patients who have a clinical condition associated with abnormal body composition includes several cross-sectional studies comparing DXA to other techniques. Relevant outcomes are symptoms and change in disease status. The available studies are primarily conducted in research settings and often use DXA body composition studies as a reference standard; these studies do not permit conclusions about accuracy of DXA for measuring body composition. More importantly, no studies were identified in which DXA body composition measurements were actively used in patient management. The evidence is insufficient to determine the effects of the technology on health outcomes.
The evidence for DXA body composition studies in patients who have a clinical condition managed by monitoring changes in body composition over time includes several prospective studies monitoring patients over time. Relevant outcomes are symptoms and change in disease status. The studies used DXA as a tool to measure body composition and were not designed to assess accuracy of DXA. None of the studies used DXA findings to make patient management decisions or addressed how serial body composition assessment might improve health outcomes. The evidence is insufficient to determine the effects of technology on health outcomes.
While DXA scans have become a valued research tool, it is unclear how information regarding body composition could be used in the active medical management of the patient to alter treatment decisions or improve health outcomes. No studies have been identified in the literature in which DXA body composition measurements were actively used in patient management, and studies have not reported data demonstrating the impact of body composition assessment on health outcomes. Therefore, the technique is considered investigational.
Bioelectrical Impedance Analysis (BIA)
Bioelectrical impedance is based on the relationship between the volume of the conductor (i.e. 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.
Studies indicate that BIA results were not as accurate, no matter which formula was used to do the calculations. For the general adult population, the relatively simple and inexpensive method of working out the BMI can produce results which are equal to, or even better, than the results of bioelectrical impedance analysis.
Based on review of the medical literature, there is currently no established role for whole body bioimpedance analysis for weight reduction or other indications. No studies have been identified in the literature in which bioimpedance analysis measurements were actively used in patient management, and studies have not reported data demonstrating the impact of body composition assessment on health outcomes. Further studies are needed to assess the clinical value of this testing.
Practice Guideline and Position Statements
International Society for Clinical Densitometry (ISCD)
In 2013, The International Society for Clinical Densitometry (ISCD) issued a statement on use of DXA body composition. The statement included the following ISCD official positions regarding the use of DXA total body composition with regional analysis:
U.S. Preventative Services Task Force Recommendations (USPSTF)
The U.S. Preventative Services Task Force (USPSTF) does not recommend DXA for body compositions analysis. In 2012, USPSTF recommended screening all adults for obesity with BMI. Its 2010 recommendation on obesity in children and adolescents recommends screening all children older than 6 years old using BMI.
American College of Cardiology (ACC)/American Heart Association (AHA)/The Obesity Society (TOS)
In 2013, the ACC/AHA/TOS issued a guideline for the management of overweight and obesity in adults and the summary of recommendations for obesity state, “identifying patients who need to lose weight (BMI and waist circumference), measure height and weight and calculate BMI at annual visits or more frequently. Measure weight circumference at annual visits or more frequently in overweight and obese adults.”
This guideline mentions no role of whole body DEXA/DXA or bioimpedance analysis in the assessment and management of overweight and obese adults.
National Institute for Health and Clinical Excellence (NICE)
In 2014, NICE issued a guideline on obesity: identification, assessment and management. The guideline included the following: “measures of overweight and obesity adult and children do not use bioimpedance as a substitute for BMI as a measure of general adiposity.”
Whole body dual x-ray absorptiometry (DXA) and whole body bioelectrical impedance analysis (BIA) for body composition studies/assessment is considered investigational for all indications.
Based on the peer reviewed medical literature there is insufficient evidence to support the use of whole body DXA and whole body bioelectrical impedance analysis (BIA) for the purpose of determining body composition. It is unclear how information regarding body composition could be used in the active medical management of the patient to alter treatment decisions or improve health outcomes. Well-designed studies evaluating the diagnostic accuracy and clinical utility of this testing are lacking. Therefore, these techniques are considered investigational.
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