Thomas L. Kelly

Dual energy X-Ray absorptiometry body composition reference values from NHANES.

In 2008 the National Center for Health Statistics released a dual energy x-ray absorptiometry (DXA) whole body dataset from the NHANES population-based sample acquired with modern fan beam scanners in 15 counties across the United States from 1999 through 2004. The NHANES dataset was partitioned by gender and ethnicity and DXA whole body measures of %fat, fat mass/height2, lean mass/height2, appendicular lean mass/height2, %fat trunk/%fat legs ratio, trunk/limb fat mass ratio of fat, bone mineral content (BMC) and bone mineral density (BMD) were analyzed to provide reference values for subjects 8 to 85 years old. DXA reference values for adults were normalized to age; reference values for children included total and sub-total whole body results and were normalized to age, height, or lean mass. We developed an obesity classification scheme by using estabbody mass index (BMI) classification thresholds and prevalences in young adults to generate matching classification thresholds for Fat Mass Index (FMI; fat mass/height2). These reference values should be helpful in the evaluation of a variety of adult and childhood abnormalities involving fat, lean, and bone, for establishing entry criteria into clinical trials, and for other medical, research, and epidemiological uses.

Dual-Energy X-Ray Performs as Well as Clinical Computed Tomography for the Measurement of Visceral Fat

Visceral adipose tissue (VAT) is associated with adverse health effects including cardiovascular disease and type 2 diabetes. We developed a dual‐energy X‐ray absorptiometry (DXA) measurement of visceral adipose tissue (DXA‐VAT) as a low cost and low radiation alternative to computed tomography (CT). DXA‐VAT was compared to VAT assessed using CT by an expert reader (E‐VAT). In addition, the same CT slice was also read by a clinical radiographer (C‐VAT) and a best‐fit anthropomorphic and demographic VAT model (A‐VAT) was developed. Whole body DXA, CT at L4–L5, and anthropometry were measured on 272 black and white South African women (age 29 ± 8 years, BMI 28 ± 7 kg/m2, waist circumference (WC) 89 ± 16 cm). Approximately one‐half of the dataset (n = 141) was randomly selected and used as a training set for the development of DXA‐VAT and A‐VAT, which were then used to estimate VAT on the remaining 131 women in a blinded fashion. DXA‐VAT (r = 0.93, standard error of the estimate (SEE) = 16 cm2) and C‐VAT (r = 0.93, SEE = 16 cm2) were strongly correlated to E‐VAT. These correlations with E‐VAT were significantly stronger (P < 0.001) than the correlations of individual anthropometry measurements and the A‐VAT model (WC + age, r = 0.79, SEE = 27 cm2). The inclusion of anthropometric and demographic measurements did not substantially improve the correlation between DXA‐VAT and E‐VAT. DXA‐VAT performed as well as a clinical read of VAT from a CT scan and better than anthropomorphic and demographic models.

DXA body composition: theory and practice.

Dual energy X-ray absorptiometry (DXA) was used to measure human body composition on a high speed fan beam scanner. High and low energy attenuation pairs, produced by the various combinations of fat mass and fat-free mass in the human body, were compared to attenuation values produced by standard materials (aluminum and acrylic). These standards were measured in various combinations to construct calibration curves for fat and fat-free mass. Primary calibration of the aluminum/acrylic combinations was achieved by direct comparison to the dual energy attenuation produced by stearic acid and pure water. Whole body examinations were accomplished using three 45 s longitudinal passes of the fan beam. These passes were acquired and assembled to create a giant, isocentric fan beam with a single center of focus. In vivo precision was 0.009 g/cm2 for BMD and 425 g for fat mass and fat-free mass (s.d.).

Assessment of abdominal fat compartments using DXA in premenopausal women from anorexia nervosa to morbid obesity.

Objective: To test a newly developed dual energy X‐ray absorptiometry (DXA) method for abdominal fat depot quantification in subjects with anorexia nervosa (AN), normal weight, and obesity using CT as a gold standard.

Validation of rapid 4-component body composition assessment with the use of dual-energy X-ray absorptiometry and bioelectrical impedance analysis.

Abstract Background The 4-component (4C) model is a criterion method for human body composition that separates the body into fat, water, mineral, and protein, but requires 4 measurements with significant cost and time requirements that preclude wide clinical use. A simplified model integrating only 2 measurements—dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA)—and 10 min of patient time has been proposed. Objective We aimed to validate a rapid, simplified 4C DXA + BIA body composition model in a clinical population. Design This was a cross-sectional observational study of 31 healthy adults. Participants underwent whole-body DXA, segmental BIA, air displacement plethysmography (ADP), and total body water (TBW) measurement by deuterium (D2O) dilution. 4C composition was calculated through the use of the Lohman model [DXA mineral mass, D2O TBW, ADP body volume (BV), scale weight] and the simplified model (DXA mineral mass and BV, BIA TBW, scale weight). Accuracy of percentage of fat (%Fat) and protein measurements was assessed via linear regression. Test-retest precision was calculated with the use of duplicate DXA and BIA measurements. Results Of 31 participants, 23 were included in the analysis. TBWBIA showed good test-retest precision (%CV = 5.2 raw; 1.1 after outlier removal) and high accuracy to TBWD2O [TBWD2O = 0.956*TBWBIA, R2= 0.92, root mean squared error (RMSE) = 2.2 kg]. %Fat estimates from DXA, ADP, D2O, and BIA all showed high correlation with the Lohman model. However, only the 4C simplified model provides high accuracy for both %Fat (R2 = 0.96, RMSE = 2.33) and protein mass (R2= 0.76, RMSE = 1.8 kg). %Fat precision from 4C DXA + BIA was comparable with DXA (root mean square-SD = 0.8 and 0.6 percentage units, respectively). Conclusions This work validates a simplified 4C method that measures fat, water, mineral, and protein in a 10-min clinic visit. This model has broad clinical application to monitor many conditions including over/dehydration, malnutrition, obesity, sarcopenia, and cachexia.