Comparison of dual-energy x-ray absorptiometry and measurement of total body water content by deuterium oxide dilution for estimating body composition in dogs

Objective - To compare percentage of body fat (%BF) estimates from dual-energy x-ray absorptiometry (DEXA) with those derived from total body water (TBW) determination by deuterium oxide (D₂O) dilution. Animals - 31 healthy, adult, purebred dogs of various ages and breeds (body weight, 15 to 39 kg). Procedure - The TBW was measured by D₂O dilution and subsequent analysis via nuclear magnetic resonance (NMR). Blood was collected before and 2 hours after IV administration of 275 mg of D₂O/kg of body weight. Plasma was separated and stored at -30 C until analysis by deuterium NMR. The DEXA scans were obtained immediately after blood collection from dogs under general anesthesia. Results - Measurements of %BF by DEXA averaged 158% higher than calculated estimates of TBW content by D₂O dilution. The linear regression of %BF by TBW content on %BF by DEXA had a slope of 1.04 and a correlation coefficient of 0.84, indicating excellent relative agreement between methods despite the significant difference in absolute agreement between the 2 methods. The average difference between methods did not differ by breed, sex, body condition score, body weight, or %BF, as measured by DEXA. Conclusion - Comparability of our data with those of previous studies suggest that DEXA is useful for in vivo estimation of body composition in healthy dogs. Body fat estimated by D₂O dilution will be less than that determined by DEXA, despite excellent relative agreement between methods.