Validation of dual energy X-ray absorptiometry (DXA) by comparison with chemical analysis of dogs and cats

Abstract

BACKGROUND: Dual-energy X-ray absorptiometry (DXA) has been used extensively to measure body composition, but has been validated by comparison to chemical analysis on relatively few occasions. Moreover, these previous validation studies have ground up entire carcasses prior to chemical analysis, thus potentially obscuring sources of error in the DXA analysis. OBJECTIVE: The purpose of this study was to validate DXA by comparison to chemical analysis in dogs and cats, performing chemical analysis on dissected rather than ground carcasses to reveal sources of discrepancy between the two methods. DESIGN: Sixteen animals (10 cats and 6 dogs weighing between 1.8 and 22.1 kg) were scanned by DXA post-mortem using a Hologic QDR-1000 W pencil beam machine and then dissected into 22 separate components. Individual tissues were dried and then sub-sampled for analysis of fat content by Soxholet extraction, or ashing in a muf¯e furnace. Body composition by DXA was compared to body composition by chemical analysis and discrepancies between the two correlated with chemical composition of individual tissues. We also explored the capability of the machine to establish the fat contents of mixtures of ground beef, lard and water. RESULTS: DXA estimates were strongly correlated with estimates derived from chemical analysis: total body mass (r 1.00), lean tissue mass (r 0.999), body water content (r 0.992) and fat mass (r 0.982). Across individuals the absolute and percentage discrepancies were also small: total body mass (13.2 g, 1.02%), lean tissue mass (119.4 g, 2.64%), water content (101 g, 1.57%) and fat content (28.5 g, 2.04%), where the percentage error is expressed relative to the average mass of that component across all individuals. Although on average DXA compared very well to chemical analysis, individual errors were much greater. Individual errors in the lean tissue and fat tissue components were strongly correlated with the fat content of skeletal muscle and the lean content of mesenteric fat. The error in the DXA estimate of total fat content was related to skeletal muscle hydration. Experimental studies using mixtures of lean ground beef, water and lard indicated that tissue hydration may have important effects on the perception of tissue fat content by DXA. Bone mineral content by DXA was approximately 30% lower than whole body ash content but only 7.7% lower than ash content of the bones. CONCLUSIONS: On average pencil beam DXA analysis using the Hologic QDR-1000 W machine provides an accurate estimate of body composition in subjects weighing between 1.8 and 22.1 kg. Individual discrepancies, however, can be large and appear to be related to lean tissue hydration.

Feline obesity - prevalence, risk factors, pathogenesis, associated conditions and assessment: a review

“…DEXA results have been shown to correlate well with the chemical analysis of body composition in cats and dogs (Speakman et al 2001). Consequently, DEXA is often used as the reference method for the assessment of body composition (Hoelmkjaer and Bjornvad 2014).…”

“…Consequently, DEXA is often used as the reference method for the assessment of body composition (Hoelmkjaer and Bjornvad 2014). However, DEXA assumes the hydration of the fat-free mass is constant and so accuracy can be affected by the level of muscle hydration (Speakman et al 2001;Jeusette et al 2010). This method has several disadvantages such as the exposure to radiation, the need for sedation, the cost, and the technical expertise required, which limits its use to the research setting (German 2010;Bjornvad et al 2011).…”

Ovariohysterectomy alters body composition and adipose and skeletal muscle gene expression in cats fed a high-protein or moderate-protein diet

“…Body composition Lean mass, fat mass and bone mineral content (BMC) were determined using DEXA (dual-energy X-ray absorptiometry), which has been previously validated in cats (Speakman et al, 2001). Determinations were conducted after ovariohysterectomy and tissue biopsy, while still under sedation.…”

Critical Appraisal of Data Acquisition in Body Composition: Evaluation of Methods, Techniques and Technologies on the Anatomical Tissue-System Level

“…More of these validations against direct values are necessary before we can be confident about the accuracy of absorptiometry (Prentice, 1995). A review of the state of the art of carcass studies related to DXA ) reveals validation attempts with rhesus monkeys (Black et al, 2001), mice (Brommage, 2003;Nagy & Clair, 2000), piglets (Chauhan et al, 2003;Elowsson et al, 1998;Koo et al, 2002Koo et al, , 2004Picaud et al, 1996;Pintauro et al, 1996), pigs (Lukaski et al, 1999;Mitchell et al, 1996Mitchell et al, , 1998, pig hind legs , chickens (Mitchell et al, 1997;Swennen et al, 2004) and with dogs and cats (Speakman et al, 2001). The majority of these validation studies were based on chemical analysis and only a few on direct dissection comparison.…”