Detection of small changes in body composition by dual-energy x-ray absorptiometry

The ability of dual-energy x-ray absorptiometry (DEXA) to detect small changes in body composition was studied in 17 men and women during a dehydration-rehydration protocol. Scale weight (BW) and total mass (TM) from DEXA were highly related (r > 0.99) as were estimates of fat-free mass (r = 0.99) and percent fat (r = 0.97) from DEXA and densitometry. Changes in BW of approximately 1.5 kg due to fluid loss and gain were highly correlated (r = 0.90) with both changes in TM and soft-tissue mass (STM) by DEXA but less so (r = 0.67) with changes in lean-tissue mass (LTM). Mean changes in TM, STM, and LTM were not different (P > 0.05) from changes in BW. Estimates of bone mass and fat were unaffected by changes in hydration. We conclude that DEXA is able to detect small individual changes in TM and STM and is also useful for detecting group changes in LTM.     

Composition analysis of pork carcasses by dual-energy x-ray absorptiometry

Dual-energy x-ray absorptiometry (DXA) was used as a noninvasive method to measure the composition of pig carcasses. A total of 181 half-carcasses (10 to 51 kg, from pigs slaughtered at approximately 30, 60, 90, and 120 kg) were scanned using a Lunar (Madison, WI) DPX-L densitometer. The DXA measurements of fat, lean, bone mineral, and total tissue mass were compared with chemical analysis for fat, water, protein, total ash, and scale weight. The mean value for total tissue mass by DXA was slightly less than the mean carcass weight (32.3 kg vs 33.6 kg, P > .05, R2 = .998). Although highly correlated (R2 = .81), the DXA measurement of the percentage of fat in the half-carcass was less (P < .001) than the chemical measurement (19.5 vs 24.9%). The DXA measurement of lean tissue mass (total mass less fat and bone mineral) was correlated with carcass protein (R2 = .97) and water (R2 = .99) content. The correlation (R2) between DXA bone mineral content and carcass ash content was only .68; however, DXA bone mineral content was more highly correlated with carcass weight (R2 = .93) than was carcass ash content (R2 = .70). When we used the DXA R value (ratio of the attenuation coefficients for fat and lean) to predict percentage of fat in the carcass, the mean value for predicted carcass fat was 25.9% (P > .05). Similarly, carcass protein and water content were predicted from DXA lean. Using DXA region of interest analysis, estimates of the fat content of the shoulder and ham regions were close to chemical values; however, DXA underestimated the fat content of the loin and side regions by 20 and 28%, respectively. When prediction equations were used to evaluate DXA measurements of the half-carcasses of 28 gilts and 37 boars slaughtered at approximately 120 kg, the half-carcasses of gilts contained more fat (33.9 vs 27.8%, P < .001), less protein (14.1 vs 16.1%, P < .001), and less water (45.9 vs 52.1%, P < .001) than those of boars. These results indicate that DXA could be a valuable research tool for measuring the composition of pig carcasses. On the basis of the results of this study, prediction equations were revised for the DXA estimation of fat, protein, and water content of the half-carcass: Fat (%) = 450 - (315 x DXA R value), Protein (g) = -145 + (.23 x DXA lean), and Water (g) = 150 + (.73 x DXA lean). Furthermore, it seems that separate prediction equations are needed for regional analysis.     

Body composition changes measured by dual-energy X-ray absorptiometry in patients receiving home parenteral nutrition

Some patients with infiltrant vesical cancer can be treated successfully with radical cysto-prostatectomy and urinary by-pass and increasingly more authors publish successful results in series of selected patients over 70- and 80-year old. Between February 1988 and July 1996, 18 radical cystectomies with orthotopic urinary by-pass were performed in the Urology Service, Policlinico Vigo, in patients over 70 (range 70-84 years), with an operative mortality rate of 11%. 8 patients (44%) developed immediate complications and 9 patients (50%) presented distant complications. Overall mortality in our series was 33.3% and survival 66.6% after a mean follow-up of 30.7 months. We believe orthotopic-continent by-pass is a valid alternative with operative mortality and complication rates similar to those of ileal ducts, with the advantage for the patient of avoiding permanent urinary stoma.     

Comparison of body composition by dual energy X-ray absorptiometry to other estimates of body composition during weight loss in obese patients with rheumatoid arthritis

Body composition was determined by dual energy X-ray absorptiometry (DXA) scanning and classical reference methods (40K, 3H2O, and a combination of these in a four-compartment model) in 19 overweight patients with rheumatoid arthritis who underwent a 12-week weight-reducing regimen. The aim of the study was to investigate whether DXA provides a valid estimate of body composition. The results showed that weight as determined by DXA was highly significantly correlated to weight determined by scales. Furthermore, significant correlations were found in the body components (fat-free mass, fat mass) determined by DXA, 40K, 3H2O and the four-compartment model. Mean values differed slightly but significantly. With respect to changes in body composition, no significant correlations were found between any of the methods, except for the weight loss recorded by DXA and scales, and loss of fat mass (and fat free mass) estimated by 3H2O and the four-compartment model. The sparseness of correlations reflected the small changes in fat-free mass and fat mass (2.6 and 1.7 kg respectively), and the fact that changes were comparable to measurement errors of the various methods. We suggest that DXA scanning is a valid supplement for determination of body composition. Validation of DXA scanning requires new experimental in vitro investigations, which, incidentally, also applies to the classical reference methods.     

Reference values of body composition obtained by dual energy X-ray absorptiometry in preterm and term neonates

We have recently reported the cDNA cloning of rat spermatidal protein TP2 and its expression in Escherichia coli using pTrc 99A as the expression vector. However, the expression level was very low. We have now improved the expression of TP2 over fivefold by (1) optimizing the codons for lysine, arginine, proline, leucine, glycine, valine, threonine, alanine, and tyrosine and (2) by engineering the vector-encoded 5' UTR. The expressed protein was in the soluble phase and could be purified to homogeneity by successive chromatography on Zinc-NTA-agarose affinity matrix and heparin agarose. Serendipitously, we have also observed a concomitant hyperinduction of vector encoded beta-lactamase gene along with TP2 in the E. coli BL21 (DE3) cells.     

Prediction of carcass and empty body composition of steers by 40K emission detection

Although originally used for prediction of whole body composition (WBC), use of 40K emission detection was later suggested for determination of empty body composition (EBC), Therefore, the present study was conducted to validate existing equations developed to predict WBC and to develop more useful equations to predict EBC or carcass composition (CC) of beef steers. Fourteen crossbred steers were detected for 40K emissions and slaughtered and their chemical composition determined from chemical analyses and total body K determined from 40K emissions. the existing equation for percentage whole body lipid had a slope of .93 and an intercept of -1.62%, indicating a close approximation of percentage of whole body lipid. Percentage of whole body protein was poorly estimated by existing equations. Equations developed for prediction of EBC relied on both BW and predicted K. Coefficients of variation for prediction of empty water or protein were within 5% and those for prediction of empty body lipid were approximately 15%. These results demonstrate that use of predicted K from 40K emission detection enhances the determination of EBC and CC.     

Prediction of percent body fat in adult males using dual energy x-ray absorptiometry, skinfolds, and hydrostatic weighing

The purpose of this study was to compare the prediction of percent body fat (%FAT) by dual energy x-ray absorptiometry (DXA), skinfolds (SF), and hydrostatic weighing (HW) in adult males. Subjects were 35 adult male Caucasians (mean +/- SD; age: 39.1 +/- 14.0 yr, height: 180.6 +/- 5.3 cm, weight: 81.0 +/- 11.1 kg). %FAT, determined by HW with residual volume determined via O2 dilution, served as the criterion. DXA %FAT was determined by the Norland XR-26 (XR-26) bone densitometer and by the SF equations of Jackson and Pollock (JP) (1978), and Lohman (LOH) (1981). Criterion referenced validation included analyzing mean (+/- SD) %FAT values using a one-way ANOVA for significance, comparison of mean differences (MD), correlations (r), standard error of estimates (SEE), and total errors (TE). Significant differences were found between means of each method. The r (0.91) and SEE (3.0 %FAT) for DXA compare favorably with the established SF methods of JP and LOH for predicting %FAT; however, DXA demonstrated the largest MD (3.9 %FAT) and TE (5.2 %FAT). Regression analysis yields HW = 0.79* DXA + 0.56. The results do not support earlier research that found no significant difference between HW and DXA %FAT in males. The study suggests the density of the fat-free body (DFFB) is not constant, and that the variation in bone mineral content affects the DFFB, which contributes to the differences between DXA and HW %FAT. We recommend further research to identify inconsistencies between manufacturers of DXA equipment in prediction of %FAT in males.     

Body composition during weight loss in obese patients estimated by dual energy X-ray absorptiometry and by total body potassium

OBJECTIVE: To validate the ability of DXA to measure total body composition before and after weight loss and the composition of the lost body mass. DESIGN: Cross sectional and follow-up study of body composition before and after a weight loss of 10.6 +/- 6.8 kg. SUBJECTS: 31 obese subjects with a mean body weight of 105.2 +/- 15.2 kg at baseline, and a mean body weight of 94.6 +/- 16.5 kg at follow-up. MEASUREMENTS: Body composition was measured by dual X-ray absorptiometry, total body potassium counting, and high precision scales before and after a weight loss. RESULTS: DXA and the scales showed a strong linear relation (r = 1). At baseline, however, DXA underestimated the body weight by a maximum of 3.2 kg because the subjects were too large for the scan table. After weight loss body weight measurements were accurate. Before and after weight loss the linear relations between DXA and TBK for FFM were strong (r = 0.92 and 0.93). Bland and Altman plots showed limits of agreement of +/-9 kg before and after weight loss; DXA underestimated FFM in women and overestimated FFM in men. DXA accounted for 80% of the lost body weight. The composition of the lost body mass did not differ from that estimated by TBK (7.6% FFM and 92.4% FM by TBK; 11% FFM and 89% FM by DXA). CONCLUSION: DXA estimates accurately the body composition and the composition of weight loss in groups of obese subjects. However, the scan table may be too small for patients weighing more than 95 kg.     

Body composition analysis by dual energy X-ray absorptiometry in female diabetics differ between manufacturers

OBJECTIVE: Comparison of body composition results by two dual energy X-ray absorptiometry (DXA) instruments, namely QDR-2000 from Hologic Inc and from Lunar in subpopulations of lean and obese subjects. DESIGN: Cross-sectional study with 85 female diabetics (BMI 18-43 kg/m2) measured with both DXA instruments. RESULTS: The regression lines for fat tissue mass (FTM), FAT% and total body bone mineral content (TBMC), but not lean tissue mass (LTM), were different from the line of identity (P < 0.01). However, the relationships were high (r2 > 0.95), and the corresponding SEE%'s were low (0.8-4.8%), and were independent of BMI. FTM and FAT% measured by the QDR-2000 were 10% higher, and LTM and TBMC 6% lower, than by DPX (P < 0.001). CONCLUSIONS: There were lack of agreements between total body composition results by DPX Lunar, and QDR-2000 Hologic Inc. Individual results on the two systems cannot be directly compared. Standardization of body composition measurements by DXA is strongly needed.     

Precision and accuracy of total body bone mass and body composition measurements in the rat using x-ray-based dual photon absorptiometry

Lean body mass (LBM), total body bone mineral mass (BMC), total body bone areal density (BMD), and body fat mass (FM) were measured in rats by dual photon absorptiometry (DXA), using two different instruments. The coefficients of variation for repeated measurements of LBM and FM were about 0.4 and 2.5%, respectively, over an animal body weight range of 150 to 600 g. For BMC and BMD, the coefficients of variation were less than 2%. The correlation coefficients for LBM, FM, BMC, and BMD measured on the two densitometers were all greater than 0.94. The slope of the regression line relating LBM measured by DXA and LBM measured by carcass analysis was 0.999, and the correlation coefficient was 0.99. For FM the slope was 1.05, and the correlation coefficient was 0.98. BMC measures by DXA were falsely low in small animals. For larger animals, the correlation between BMC and ash weight was 0.93, but the slope of the regression line was 0.78. DXA measures of LBM and FM were accurate and reproducible for rats weighing between 150 and 600 g. There was a size-dependent error in BMC, which will be significant in longitudinal measurements of bone mass.     

Impact of hydration status on body composition as measured by dual energy X-ray absorptiometry in normal volunteers and patients on haemodialysis

To evaluate the influence of hydration status on the estimation of body composition using dual-energy X-ray absorptiometry (DXA), six normal volunteers and seven patients on maintenance haemodialysis were investigated using two different DXA machines (Lunar DPX, Hologic QDR 1000/W). Normal volunteers were studied (Hologic QDR 1000/W) before and 1 h after ingestion of breakfast, lunch and dinner (drinking various amounts of liquids at each meal, 0.5-2.4 kg). Whereas bone mineral content and body fat mass did not change, lean body mass of the trunk increased as a consequence of the meals. Conversely in patients on haemodialysis (Lunar DPX), lean body mass decreased in all segments of the body as a consequence of removal of 0.9-4.4 kg of salt-containing fluid by haemodialysis (trunk 61%, legs 30%, arms 5.5% and rest of the body 3.5%), whereas bone mineral content and body fat mass remained unchanged. However, this finding(s) did not hold true in one particular patient with bilateral hip prostheses. Measurement of body composition in eight normal volunteers on the same day with both machines showed similar results for lean and fat mass, whereas bone mineral content was found to be 17% higher using the Lunar DPX. In summary, in centres where both machines are available, follow-up of one individual patient should always be performed using the same equipment. In addition, hydration status and food intake must be taken into account when repetitive measurements of lean body mass are performed in the same patient.     

Segmental body composition assessed by bioelectrical impedance analysis and DEXA in humans

The present study assessed the relative contribution of each body segment to whole body fat-free mass (FFM) and impedance and explored the use of segmental bioelectrical impedance analysis to estimate segmental tissue composition. Multiple frequencies of whole body and segmental impedances were measured in 51 normal and overweight women. Segmental tissue composition was independently assessed by dual-energy X-ray absorptiometry. The sum of the segmental impedance values corresponded to the whole body value (100.5 +/- 1.9% at 50 kHz). The arms and legs contributed to 47.6 and 43.0%, respectively, of whole body impedance at 50 kHz, whereas they represented only 10.6 and 34.8% of total FFM, as determined by dual-energy X-ray absorptiometry. The trunk averaged 10.0% of total impedance but represented 48.2% of FFM. For each segment, there was an excellent correlation between the specific impedance index (length2/impedance) and FFM (r = 0.55, 0.62, and 0.64 for arm, trunk, and leg, respectively). The specific resistivity was in a similar range for the limbs (159 +/- 23 cm for the arm and 193 +/- 39 cm for the leg at 50 kHz) but was higher for the trunk (457 +/- 71 cm). This study shows the potential interest of segmental body composition by bioelectrical impedance analysis and provides specific segmental body composition equations for use in normal and overweight women.     

Body composition by X-ray absorptiometry and bioelectrical impedance in chronic respiratory insufficiency patients

Nutrition assessment is important during chronic respiratory insufficiency to evaluate the level of malnutrition or obesity and should include body composition measurements. The appreciation of fat-free and fat reserves in patients with chronic respiratory insufficiency can aid in designing an adapted nutritional support, e.g., nutritional support in malnutrition and food restriction in obesity. The purpose of the present study was to cross-validate fat-free and fat mass obtained by various bioelectric impedance (BIA) formulas with the fat-free and fat mass measured by dual-energy X-ray absorptiometry (DXA) and determine the formulas that are best suited to predict the fat-free and fat mass for a group of patients with severe chronic respiratory insufficiency. Seventy-five patients (15 women and 60 men) with chronic obstructive and restrictive respiratory insufficiency aged 45-86 y were included in this study. Body composition was calculated according to 13 different BIA formulas for women and 12 for men and compared with DXA. Because of the variability, calculated as 2 standard deviations, of +/- 5.0 kg fat-free mass for women and +/- 6.4 kg for men for the best predictive formula, the use of the various existing BIA formulas was considered not clinically relevant. Therefore disease-specific formulas for patients with chronic respiratory insufficiency should be developed to improve the prediction of fat-free and fat mass by BIA in these patients.     

Cross-sectional and longitudinal evaluation of body composition in men with HIV infection

We report a case of subcutaneous phaeohyphomycosis observed in a male patient presenting pulmonary sarcoidosis and submitted to corticosteroid treatment. He presented nodular erythematous-violaceous skin lesions in the dorsum of the right hand. Histopathological examination of the biopsied lesion revealed dematiaceous hyphae and yeast-like cells, with a granulomatous tissual reaction. The isolated fungus was identified as Phoma cava. A review of the literature on fungal infection caused by different Phoma species, is presented. The patient healed after therapy with amphotericin B. followed by itraconazole.