Assessing body composition in taller or broader individuals using dual-energy X-ray absorptiometry: a systematic review

Abstract Background/objectives: Dual-energy X-ray absorptiometry (DXA) is an accurate and reliable method for determining body composition, but a limiting feature is the restricted scanning areas (∼190 × 60 cm2). This shortcoming is relevant not only to athletes involved in sports where height is a major performance determinant but also to obese individuals with a large trunk mass and breadth in whom body dimensions frequently exceed the scan area. This study reviews solutions for DXA length and/or width limitations and its accuracy for body composition assessment using the PRISMA statement guidelines. Subjects/methods: Reviewed studies included English language articles from MEDLINE and Thomson Reuters Web of Knowledge platform (1990–2013), and were selected if procedures to overcome the scan area limitations and its validity in assessing the body composition of healthy participants were addressed. Search terms included: DXA, scan, height, width, length, wide, large, tall and obese. Results: A total of seven studies met the criteria and were selected. The sum of two DXA scans and adopting a knee-bent position are alternative procedures proposed for evaluating individuals using pencil and fan-beam Hologic instruments, who are taller than the scan area, whereas a half-body scan is recommended for overcoming the limitations of whole-body measurements in subjects who are wider than the scan area width of Lunar densitometers. Conclusions: Overall, the proposed procedures are useful and valid, in particular the half-body scan alternative, which avoids unnecessary radiation exposure and scanning time. However, these alternatives were developed for specific densitometers, models and scan mode, and applicability to other instruments requires further research. Introduction Assessment of body composition is important for achieving a better understanding of nutritional status and disease processes, and for evaluating treatments and interventions. Likewise, body composition is a factor that can influence athletic performance and, as such, is of considerable interest to athletes and coaches. Several different body composition methods can be applied in the clinical setting.1 One traditional research approach2, 3 is to evaluate a subject’s fat mass (FM) based on a two-compartment model, in which the subject’s body mass is partitioned into FM and fat-free mass, using densitometric methods. The addition of total body water estimation using isotope dilution allows the development of a three-compartment model,3 which can be extended into a four-compartment model by the addition of an estimate of bone mineral content (BMC) using dual-energy X-ray absorptiometry (DXA).4, 5 Investigators, in general, agree that multi-compartment models provide the criterion measurements for body composition assessment,4, 5, 6, 7 but their costly, time-consuming and sophisticated technological analysis limit their use at the clinical settings. An important advance in body composition research is the availability of DXA for partitioning body mass into three components: FM, lean soft tissue (LST) and BMC,8 quantifying with precision9, 10, 11, 12 total and regional FM, LST and BMC, and providing accurate measures when compared with four-compartment models.5, 13, 14, 15, 16, 17, 18, 19, 20 Indeed, DXA is a time-efficient and minimal-risk method that has allowed its wide implementation and usage in large multi-center studies, including the National Health and Nutrition Examination Survey.21, 22 However, although DXA has high precision and overall accuracy in body composition assessment, there remain concerns that need to be addressed. The purpose of the present study is to review the major limitations of assessing body composition in individuals who exceed the scan area dimensions and to provide alternative techniques, published between 1990 and 2013, and their respective accuracies for overcoming these limitations. Materials and methods Protocol, search strategy and selection criteria An extensive literature review was conducted in accordance with the guidelines proposed in the PRISMA statement,23 to select procedures to overcome DXA scan area limitations, including their detailed validation parameters. MEDLINE database (OVID, PubMed), the Thomson Reuters Web of Knowledge platform and a personal library were searched for English language articles published in peer-reviewed journals since 1990, with the last search run on 11 April 2013. The keyword search terms included: dual-energy X-ray absorptiometry, scan, height, width, length, wide, large, tall and obese. The following characteristics and criteria were used: (1) healthy participants, (2) procedures to overcome the DXA scan area (width or length) in assessing FM, LST and BMC and (3) description of the statistical methods used to validate the procedure. For the identification of the studies, the process included the following steps: screening of the identified records, examination of the full text of potentially relevant studies and application of the eligibility criteria to select the included studies. For assessing eligibility, studies were screened independently in an unblinded standardized manner by the primary author, whereas the secondary author examined a small sample of them. Results A total number of seven studies were identified in the review. Our search provided a total of 447 citations. Of these, 430 studies were discarded, because after reviewing the title and abstract it appeared that these papers clearly did not meet the criteria. The full text of the remaining 17 citations was examined in more detail. From the 17 studies, 10 studies did not meet the inclusion criteria described in the Materials and Methods section. A flow diagram is illustrated in Figure 1 to describe the number of studies screened, assessed for eligibility and included in the review, along with reasons for exclusions at each stage. Figure 1 Flow of information through the different phases of the systematic review. Full size image The included studies cover selected procedures to overcome DXA scan area limitation, and detailed validation parameters extracted from each publication (Tables 2 and 3) are synthesized under three main sections: DXA limitations, overcoming DXA limitations and statistical considerations. DXA limitations In a recent review, Toombs et al.24 pointed out the main DXA technological advances, in particular the progressive replacement of the original pencil-beam densitometers by fan-beam devices that allowed for better resolution and faster scan times. The authors generally highlighted DXA as a convenient and useful diagnostic tool for body composition assessment.24 As described by Brownbill and Ilich,25 the three major commercial manufacturers of densitometers are GE Medical Systems Inc. (former Lunar), Madison, WI, USA; Hologic Inc., Waltham, MA, USA; and Cooper-Surgical (former Norland Medical Systems, Inc.), Trumbull, CT, USA (...truncated)