Body fat and fat-free mass measured by bioelectric impedance spectroscopy and dual-energy X-ray absorptiometry in obese and non-obese adults

The aim of the present study was to compare body fat mass (FM) and fat-free mass (FFM) estimates by bioelectric impedance spectroscopy (BIS), with respective estimates by dual-energy X-ray absorptiometry (DXA), in obese and non-obese subjects. Body composition was measured in ninety-three obese and non-obese men and women by BIS device, BodyScout (Fresenius Kabi, Bad Homburg, Germany) and DXA device, Lunar iDXA (GE Healthcare, Madison, WI, USA). Mean difference between the methods was analysed by t tests, and Bland-Altman plots were generated to further examine the differences between the methods. Mean difference between the estimates by DXA and BIS (ΔDXA - BIS and Bland-Altman 95 % limits of agreement) were as follows: FM 4·1 ( - 2·9, 11·2) kg and 4·5 ( - 2·9, 11·8) %, FFM - 4·1 ( - 11·2, 2·9) kg and - 4·5 ( - 11·9, 2·9) %, indicating large inter-individual variation and statistically significant underestimation of FM and overestimation of FFM by BIS, as compared to DXA. The underestimation of FMkg (FM measured in kg) and overestimation of FFMkg (FFM measured in kg) were more pronounced in men than in women, and the underestimation of FM% (FM measured in percent) and overestimation of FFM% (FFM measured in percent) were more pronounced in normal weight (BMI = 20·0-24·9 kg/m2) than in overweight and obese (BMI ≥ 25·0 kg/m2) subjects. BIS may be suitable for classification of a population into groups according to FM and FFM. However, the large inter-individual variation suggests that this BIS device with the proprietary software is insufficient for estimation of single individual body FM and FFM.     

Body composition in patients with an ileostomy and inflammatory bowel disease: validation of bio-electric impedance spectroscopy (BIS)

OBJECTIVE: To validate bio-electric impedance spectroscopy (BIS) by comparison with other methods for determination of body water compartments in stable subjects with an ileostomy and no or minor small bowel resection for inflammatory bowel disease (IBD). SUBJECTS: Twenty-one subjects were included, age range 36-65 y (female/male=12/9), Crohn's disease (CD), n=14, ulcerative colitis (UC), n=6 and indeterminate colitis (IDC), n=1. METHODS: Fluid compartments were assessed by the use of three independent methods: BIS, dual-energy X-ray absorptiometry (DXA) and dilution techniques (DIL); tritiated water (total body water, TBW); and bromide (extracellular water, ECW), respectively. Intra-cellular water (ICW) was calculated as TBW-ECW. For comparison TBW was also predicted according to an empirical formula. Differences were analysed using Bland-Altman plots. RESULTS: The mean TBW values obtained from the impedance measurement differed in the order of -2.21 (DIL) to 1.41 (DXA) in women and -2.01 (DIL) to 2.61 (DXA) in men, from the measured and derived values of total body water. Prediction of TBW gave values that were close to BIS, with a mean difference of -0.31 in male subjects and +0.51 in female subjects.Assessment of ECW revealed that the mean difference between dilution and impedance was less in women than in men (P<0.01). CONCLUSION: The differences between all methods to assess fluid compartments are pronounced. To further investigate the use of the method in clinical practice for dynamic monitoring of rehydration in ileostomates with acute diarrhoea, repeated measurements together with comparison with weight fluid-balance charts are suggested. SPONSORSHIP: The study was supported by grants from the Swedish Medical Research Council (17X-03117), G?teborgs L?kars?llskap and IB and A Lundbergs forskningsstiftelse.     

Dual-energy X-ray absorptiometry for body composition estimation in Chinese women

OBJECTIVE: To determine whether dual-energy X-ray absorptiometry (DXA) is a valid method for body composition assessment of obese and non-obese subjects. DESIGN: Cross-sectional study. SUBJECTS: Chinese women living in Hong Kong; 66 of 91 subjects had body mass index (BMI) of >25 kg/m2. MEASUREMENTS: Anthropometrics, including body weight, body height, waist and hip girth. Percentage body fat (%BF) and fat-free mass (FFM) from DXA (Hologic 2000 plus, Enhanced Array Whole Body Version 5.63) were compared with that based on a tracer dose of deuterium oxide for the determination of total body water (TBW). RESULTS: In both obese and non-obese subjects, FFMDXA was similar to FFMTBW. The Bland and Altman-type analysis indicated that comparable between-methods differences (mean bias) and limits of agreement were obtained in obese and non-obese subjects for FFM (0.4, between -4.4 and 5.2 kg vs 0.5, between -3.1 and 4.1 kg) and %BF (-0.6, between -7.6 and 6.4% vs -1.2, between -8.6 and 6.2%). The %BF bias was independent of age, BMI, hip circumference, and waist-to-hip ratio, but correlated with waist girth (r=0.24, P=0. 021). CONCLUSION: The sources of bias are methodological and anthropometric in nature. The between-methods differences, however, are small and clinically insignificant. DXA is a valid method for assessing the body composition of obese patients. SPONSORSHIP: This study was supported by a HKU-CRCG grant.     

Impact of indexing resting metabolic rate against fat-free mass determined by different body composition models

OBJECTIVE: To examine the differences arising from indexing resting metabolic rate (RMR) against fat-free mass (FFM) determined using two-, three- and four-compartment body composition models. DESIGN: All RMR and body composition measurements were conducted on the same day for each subject following compliance with premeasurement protocols. SUBJECTS: Data were generated from measurements on 104 males (age 32.1+/-12.1 y (mean+/-s.d.); body mass 81.15+/-12.85 kg; height 179.5+/-6.5 cm; body fat 20.6+/-7.6%). INTERVENTIONS: Body density (BD), total body water (TBW) and bone mineral mass (BMM) were measured by hydrodensitometry, deuterium dilution and dual energy X-ray absorptiometry (DXA), respectively. These measures were used to determine two (hydrodensitometry: BD; hydrometry: TBW)-, three (BD and TBW)- and four- compartment (BD, TBW and BMM) FFM values. DXA also provided three compartment derived FFM values. RMR was measured using open circuit indirect calorimetry. RESULTS: Three (body fat group: lean, moderate, high) x five (body composition determination: hydrodensitometry, hydrometry, three-compartment, DXA, four-compartment) ANOVAs were conducted on FFM and RMR kJ.kg FFM(-1).d(-1). Within-group comparisons revealed that hydrodensitometry and DXA were associated with significant (P<0.001) overestimations and underestimations of FFM and RMR kJ.kg FFM(-1).d(-1), respectively, compared with four-compartment-derived criterion values. A significant interaction (P<0.001) resulted from DXA's greater deviations from criterion values in lean subjects. While hydrometric means were not significantly (P> or =0.68) different from criterion values intraindividual differences were large (FFM: -1.5 to 2.9 kg; RMR: -6.0 to 3.2 kJ.kg FFM(-1).d(-1)). CONCLUSION: The relationship between RMR kJ.kg FFM(-1).d(-1) and exercise status would best be investigated using three (BD, TBW)- or four (BD, TBW, BMM)-compartment body composition models to determine FFM. Other models either significantly underestimate indexed RMR (hydrodensitometry, DXA) or display large intraindividual differences (hydrometry) compared with four-compartment derived criterion values. SPONSORSHIP: Australian Research Council (small grants scheme).     

Body composition in children with bronchopulmonary dysplasia predicted from bioelectric impedance and anthropometric variables: comparison with a reference dual X-ray absorptiometry

Since children with bronchopulmonary dysplasia often suffer from malnutrition and growth failure, evaluation of body composition is a very important tool to nutritional support. The aim of this study was to compare assessment of fat-mass (FM) and fat-free mass (FFM), evaluated by bio-impedancemetry and anthropometry compared to dual-X-ray-absorptiometry (DXA) in children with bronchopulmonary dysplasia. PATIENTS: Seventy-one children, aged 4-8 years, with bronchopulmonary dysplasia were enrolled. METHODS: FM and FFM measured using anthropometry and bio-impedancemetry were compared to FM and FFM obtained by DXA using the Bland-Altman method. RESULTS: Both bio-impedancemetry and anthropometry gave good agreement with DXA to evaluate FM and FFM. Anthropometry method, in general, slightly under-estimated FM (mean difference: -0.02 kg, standard deviation: 0.99) and FFM (mean difference: -0.70 kg+/-1.72). Bio-impedancemetry method overestimated FM (mean difference: 0.34 kg+/-2.06) and underestimated FFM (mean difference: -1.24 kg+/-3.32). CONCLUSION: In children with bronchopulmonary dysplasia aged, 4-8 years, both anthropometry and bio-impedancemetry cannot be used to precisely evaluate body composition.     

Comparison of the effectiveness of 2 dual-energy X-ray absorptiometers with that of total body water and computed tomography in assessing changes in body composition during weight change

BACKGROUND: Little information is available on the assessment of changes in body composition as a function of weight change with the use of the fan beam of dual-energy X-ray absorptiometry (DXA). OBJECTIVE: The objective was to determine the accuracy of the fan beam of the QDR 4500A densitometer and the pencil beam of the QDR 2000 densitometer in estimating changes in whole-body lean soft tissue mass (LSTM(DXA)) and fat mass (FM) with weight change. DESIGN: Thirty-seven subjects who lost 5.7 +/- 4.5 kg were measured before and after weight change. Using total body water and computed tomography (CT) of the midthigh, we compared changes in FFM(TBW) and LSTM(CT) with changes in LSTM(DXA). RESULTS: Overall, compared with TBW, the fan beam gave a larger estimate of change (macro x +/- SD) in LSTM (fan beam - TBW: -0.7 +/- 1.6 kg) than did the pencil beam (pencil beam - TBW: -0.1 +/- 1.6 kg). When the change in LSTM obtained with the fan beam and pencil beam was regressed against the change in FFM(TBW), the slope of the line for the fan beam was 0.97 (r(2) = 0.61) and that for the pencil beam was 0.86 (r(2) = 0.61). Regression analysis showed that the results between the 2 units were not interchangeable. For the midthigh region, the change in LSTM(CT) was moderately correlated with the change in LSTM(DXA) with the fan beam and pencil beam. CONCLUSIONS: The measurement of change in LSTM with the fan and pencil beams provides the same relation to changes in FFM assessed by TBW, but the 2 systems are not interchangeable.     

生物电阻抗法测量7～10岁儿童总体水含量和去脂体重的预测模型

目的利用生物电阻抗方法测量儿童的体成分,建立适合我国儿童体成分的预测方程。方法在北京市采用目的抽样法选取409名7～10岁的儿童（男生220名,女生189名）,测量身高和体重,采用生物电阻抗仪测量全身电阻抗和电容抗,采用单标水法测量的总体水（totalbodywater,TBW）和去脂体重（fat—freemass,FFM）作为标准,用多元线性逐步回归法建立回归方程,并采用纯误差和Bland—Altman分析法来判断预测方程的准确度。结果TBW的预测方程=-6．893＋0．410x性别（男：1,女=0）＋0．273×年龄（岁）＋0．174x体重（k）＋0．081×身高（cm）＋0．206x阻抗指数（cm2/Ω）（R2=0．90,均方根误差=1．2kg）;FFM的预测方程=-9．742＋0．784x性别（男=1,女=0）＋0．429x年龄（岁）＋0．227×体重（kg）＋0．104x身高（cm）＋0．269×阻抗指数（cm2／Ω）（R2=0．90,均方根误差=1．6kg）。TBW和FFM的预测值与测量值间差异均无统计学意义,纯误差分别是1．4、1．8kg。TBW和FFM的测量值与预测值的差值与均值之间存在显著正相关性（相关系数分别为0．24、0．23,P〈0．01）。不同BMI分组的测量值与预测值间差异均无统计学意义。结论推导的预测方程有较高的精确度和准确度,能有效准确地预测我国7～10岁儿童的体成分。     

Body composition assessment in adults with cystic fibrosis: comparison of dual-energy X-ray absorptiometry with skinfolds and bioelectrical impedance analysis

OBJECTIVE: We compared body composition measurement in adults with cystic fibrosis (CF) by using non-invasive methods (skinfold thicknesses and bioelectrical impedance analysis [BIA]) with dual-energy X-ray absorptiometry (DXA). METHODS: Seventy-six adults with CF (mean age 29.9 +/- 7.9 y, mean body mass index 21.5 +/- 2.5 kg/m(2)) were studied. Body composition was measured to calculate fat-free mass (FFM) using DXA, the sum of four skinfold thicknesses, and BIA (predictive equations of Lukaski and of Segal). RESULTS: Mean FFM values +/- standard deviation measured using DXA were 54.8 +/- 7.3 kg in men and 41.2 +/- 3.9 kg in women. Mean FFM values measured using BIA/Lukaski were 51.5 +/- 7.8 kg in men and 40.4 +/- 4.9 kg in women (P < 0.0005 for men, not significant for women for comparison with DXA). Mean FFM values measured using BIA/Segal were 54.2 +/- 7.5 kg for men and 44.1 +/- 5.9 kg for women (not significant for men, P < 0.0005 for women for comparison with DXA). Mean FFM values measured using skinfolds were significantly higher than those for FFM with DXA (57.2 +/- 7.2 kg in men, 43.3 +/- 4.3 kg in women, P < 0.0005 for comparison with DXA). The 95% limits of agreement with FFM using DXA were, for men and women, respectively, -8.3 to 1.7 kg and -6.4 to 4.8 kg for BIA/Lukaski, -4.8 to 3.6 kg and -3.1 to 8.9 kg for BIA/Segal, and -2.8 to 7.3 kg and -1.5 to 5.7 kg for skinfolds. CONCLUSION: This study suggests that skinfold thickness measurements and BIA will incorrectly estimate FFM in many adults with CF compared with DXA measurements of FFM. These methods have limited application in the assessment of body composition in individual adult patients with CF.     

Comparison of isotope dilution with bioimpedance spectroscopy and anthropometry for assessment of body composition in asymptomatic HIV-infected and HIV-uninfected breastfeeding mothers

BACKGROUND: The effect of breastfeeding on the nutrition of HIV-infected (HIV+) mothers is unknown. Simple, valid methods are needed for body-composition assessment of HIV+ women. OBJECTIVE: We compared the ability of bioimpedance spectroscopy (BIS) and anthropometry with that of isotope dilution (2H2O) to measure fat-free mass (FFM) and fat mass (FM) in HIV+ and HIV-uninfected (HIV-) breastfeeding South African mothers. DESIGN: Total body water (TBW) content of 68 lactating mothers (20 HIV+, 48 HIV-) was measured 10 wk after delivery by using BIS and 2H2O to measure FFM and FM. Anthropometric measurements included body mass index (BMI; in kg/m2), midupper arm circumference (MUAC), and 4 skinfold thicknesses. RESULTS: TBW, FFM, and FM measurements determined by BIS were correlated with 2H2O measurements in HIV+ (r = 0.664, 0.621, and 0.872, respectively; P < 0.01) and HIV- (r = 0.876, 0.868, and 0.932, respectively; P < 0.001) mothers. TBW measured by BIS was greater than that measured by the 2H2O method in both HIV+ (1.8 L) and HIV- (1.5 L) women; FM or FFM did not differ significantly by method. BMI, MUAC, and all skinfold-thickness measurements correlated strongly (r > 0.62, P < 0.001) with FM measured by 2H2O in both groups. BMI and MUAC correlated (r > 0.64, P < 0.001) with FFM in HIV- mothers but not in HIV+ mothers. CONCLUSIONS: In HIV+ and HIV- breastfeeding mothers, BIS provides an estimate of body composition comparable to that obtained with the 2H2O method. BMI and MUAC are useful in predicting FM in both groups but are not valid measures of FFM in HIV+ mothers.     

Measurement of body water by multifrequency bioelectrical impedance spectroscopy in a multiethnic pediatric population.

BACKGROUND: Bioelectrical impedance spectroscopy (BIS) may provide a noninvasive, rapid method for the assessment of total body water (TBW), extracellular water (ECW), and intracellular water (ICW). Few studies, however, have examined the accuracy of BIS in pediatric populations. OBJECTIVE: Our objective was to evaluate the accuracy of BIS for the measurement of TBW, ECW, and ICW in healthy children. DESIGN: Dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), and BIS measurements were performed in 347 children (202 males and 145 females aged 4-18 y). The reference values for TBW, ECW, and ICW were defined by using a DXA+TBK model. BIS values were evaluated by using the method of Bland and Altman. A randomly selected calibration group (n = 231) was used to derive new BIS constants that were tested in the remaining group (n = 116). RESULTS: BIS values were highly correlated with the reference values (r(2) = 0.94-0.97, P < 0.0001), but differences between the BIS and DXA+TBK models for individuals were significant (P < 0.001). Use of new BIS constants reduced the mean differences between the BIS and DXA+TBK models; the SDs of the mean differences were improved (1.8 L for TBW, 1.4 L for ICW, and 1.0 L for ECW) for the total population. CONCLUSIONS: On a population basis, BIS can be calibrated to replace the DXA+TBK model for the assessment of TBW, ECW, and ICW in healthy children. The accuracy of the BIS measurement in individual children may be refined further by using age- and sex-specific adjustments for the BIS calibration constants.     

Body composition following stem cell transplant: Comparison of bioimpedance and air-displacement plethysmography

ObjectiveThe aim of this study was to assess the agreement between detected changes in body composition determined by bioimpedance spectroscopy (BIS) and air-displacement plethysmography (ADP) among patients with cancer undergoing peripheral blood stem cell transplantation (PBSCT); and to assess the agreement of absolute values of BIS with ADP and dual energy x-ray (DXA).MethodsForty-four adult hematologic cancer patients undergoing PBSCT completed both BIS and ADP assessment at preadmission and at 3 mo after transplantation. A subsample (n = 11) was assessed by DXA at 3 mo after transplantation. Results were examined for the BIS instrument’s default setting and three alternative predictive equations from the literature. Agreement was assessed by the Bland-Altman limits of agreement analysis while correlation was examined using the Lin’s concordance correlation.ResultsChanges in body composition parameters assessed by BIS were comparable with those determined by ADP regardless of the predictive equations used. Bias of change in fat-free mass was clinically acceptable (all <1 kg), although limits of agreement were wide (more than ±6 kg). Overall, the BIS predictive equation accounting for body mass index performed the best. Absolute body composition parameters predicted by the alternative predictive equations agreed with DXA and ADP better than the BIS instrument’s default setting.ConclusionChanges predicted by BIS were similar to those determined by ADP on a group level; however, agreement of predicted changes at an individual level should be interpreted with caution due to wide limits of agreement.     

Validation of a three-frequency bioimpedance spectroscopic method for body composition analysis

OBJECTIVE: We assessed whether whole-body multiple frequency impedance (MFBIA) data obtained at a few discrete frequencies could be used to estimate accurately resistance at 0 (R(0)) and infinite (R(infinity)) frequencies required for prediction of body composition by mixture theory. METHODS: Fat-free mass (FFM) was measured in 157 subjects (77 males, 80 females; body mass index [BMI] 17.8-41.7 kg/m(2)) by dual X-ray absorptiometry (DXA). Whole-body impedance was measured and R(0) and R(infinity) were calculated by three different methods. FFM predicted using the different values of R(0) and R(infinity) were compared with each other and with the reference DXA values for all subjects stratified according to BMI band (BMI <24.9 kg/m(2), normal weight; BMI 25-29.9 kg/m(2), overweight; BMI >30 kg/m(2), obese). RESULTS: All BIA procedures predicted an FFM that was slightly but significantly different from DXA-derived values, underestimating by 0.24 to 1.4 kg in the normal-weight subjects and overestimating by 5.3 to 7.1 kg in the obese subjects. Although statistically significant, the different impedance procedures were highly correlated (r > 0.98), with small limits of agreement (approximately +/-2%) when used to predict FFM. Predictive power was associated with BMI, worsening as BMI increased. CONCLUSION: MFBIA can be used to estimate impedance parameters required for mixture theory prediction of body composition, but this approach requires adjustment for BMI to be accurate.     

Evaluation of a new bioelectrical impedance instrument for the prediction of body cell mass independently of height or weight

The objective of the present study was to evaluate the performance of a new bioelectrical impedance instrument, the Soft Tissue Analyzer (STA), which predicts a subject's body composition. A cross-sectional population study in which the impedance of 205 healthy adult subjects was measured using the STA. Extracellular water (ECW) volume (as a percentage of total body water, TBW) and fat-free mass (FFM) were predicted by both the STA and a compartmental model, and compared according to correlation and limits of agreement analysis, with the equivalent data obtained by independent reference methods of measurement (TBW measured by D(2)O dilution, and FFM measured by dual-energy X-ray absorptiometry). There was a small (2.0 kg) but significant (P < 0.02) difference in mean FFM predicted by the STA, compared with the reference technique in the males, but not in the females (-0.4 kg) or in the combined group (0.8 kg). Both methods were highly correlated. Similarly, small but significant differences for predicted mean ECW volume were observed. The limits of agreement for FFM and ECW were -7.5-9.9 and -4.1-3.0 kg, respectively. Both FFM and ECW (as a percentage of TBW) are well predicted by the STA on a population basis, but the magnitude of the limits of agreement with reference methods may preclude its usefulness for predicting body composition in an individual. In addition, the theoretical basis of an impedance method that does not include a measure of conductor length requires further validation.     

生物电阻抗法和双能X线吸收法测量7~ 17岁儿童青少年体成分的一致性评价

目的评价生物电阻抗法(BIA)与双能X线吸收法(DXA)测量7~17岁儿童青少年体成分的一致性。方法对1431名儿童进行BIA和DXA检测。采用组内相关系数(ICC)和Bland-Altman分析评价方法间所测去脂体重和脂肪量的一致性。Bland-Altman分析在对数变换的数据中进行。结果男、女生中BIA与DXA所测去脂体重的ICC分别为0.986和0.974,脂肪量的ICC则分别为0.854和0.926。男生中BIA与DXA的去脂体重比值均值及一致性界限(LoA)分别为1.04和0.95~1.14,女生中则为1.02和0.90~1.15。男、女生中去脂体重的LoA范围均随年龄增长而变窄。男、女生中两种方法的脂肪量比值LoA范围均较宽,分别为0.40~1.27和0.48~1.48。此外,男、女生中均可看到各成分的比值LoA范围随BMI等级增高而变窄。结论BIA所测去脂体重与DXA的一致性良好,但BIA测量脂肪量的误差较大。肥胖儿童的BIA与DXA一致性优于消瘦和正常体重儿童。     

Total body protein in healthy adolescent girls: validation of estimates derived from simpler measures with neutron activation analysis

BACKGROUND: Little recent and accurate information about body protein content in healthy adolescent girls is available. OBJECTIVE: The objective was to assess the total body nitrogen (TBN) and total body protein (TBPr) contents of fat-free mass (P:FFM) in a group of healthy adolescent girls and to validate previously published TBN prediction equations. DESIGN: TBN was measured with in vivo neutron activation analysis (TBNNAA). Bone mineral density and FFM were measured with dual-energy X-ray absorptiometry (FFMDXA), total body water and FFM were measured with bioimpedance analysis, and FFM was assessed by measuring skinfold thicknesses in 51 girls with a mean (+/- SD) age of 14.7 +/- 0.7 y. The validity of the TBN prediction equations was assessed with Bland-Altman analysis. RESULTS: TBNNAA in our adolescent group was higher (1.49 kg) than values reported in earlier studies of women (1.25 and 1.31 kg), and P:FFM was slightly higher (23%) than that documented in adults (19-21%). Previously published TBN equations showed either systematic bias or wide limits of agreement. CONCLUSION: A predictive equation derived from the present study population based on FFMDXA improves the prediction of TBN for groups of young girls but may not be helpful for individuals in clinical settings.     

Evaluation of foot-to-foot bioelectrical impedance analysis for the prediction of total body water in oncology outpatients receiving radiotherapy

OBJECTIVE: To investigate the accuracy of total body water (TBW) predicted by foot-to-foot bioelectrical impedance compared with a deuterium oxide dilution technique in oncology outpatients receiving radiotherapy. DESIGN: Cross-sectional design. SETTING: Two private Australian radiation oncology facilities. SUBJECTS: In all, 27 subjects (23 males; four females); mean age 62 (+/-15) y; mean BMI 26.2 kg/m2 (+/- 3.6). INTERVENTION: TBW was measured using a deuterium oxide dilution technique and predicted using foot-to-foot bioelectrical impedance (Tanita Inc., Tokyo, Japan, Models TBF 410 and 300GS). RESULTS: The mean (s.d.) values for predicted and measured TBW was 41.5 (6.7) and 39.7 (8.7) l, respectively, indicating a mean bias to overestimation by the foot-to-foot impedance of 1.8 l. However, a significant negative correlation between the mean of the measurements of TBW and their difference (r=-0.40; P=0.04) indicates a progressive underestimation of TBW by foot-to-foot impedance as the water content of the body increases. The analysis of 95% limits of agreement (+/-2 s.d.) showed that for most individuals the TBW predicted by foot-to-foot impedance can vary as much as 12 l above or 8.6 l below the actual TBW measured by a deuterium oxide dilution technique. CONCLUSION: There is good agreement between foot-to-foot bioelectrical impedance with a gold standard technique at the group level. However, the significant correlation between the difference of predicted and measured TBW, and the wide limits of agreement between the two methods, indicates that the use of foot-to-foot impedance in assessing TBW may lead to unacceptable error in individuals.     

Development of bioelectrical impedance analysis prediction equations for body composition with the use of a multicomponent model for use in epidemiologic surveys

BACKGROUND: Previous studies to develop and validate bioelectrical impedance analysis (BIA) equations to predict body composition were limited by small sample sizes, sex specificity, and reliance on reference methods that use a 2-component model. OBJECTIVE: This study was designed to develop sex-specific BIA equations to predict total body water (TBW) and fat-free mass (FFM) with the use of a multicomponent model for children and adults. DESIGN: Data from 5 centers were pooled to create a sample of 1474 whites and 355 blacks aged 12-94 y. TBW was measured by dilution, and FFM was estimated with a multicomponent model based on densitometry, isotope dilution, and dual-energy X-ray absorptiometry. RESULTS: The final race-combined TBW prediction equations included stature(2)/resistance and body weight (R(2) = 0.84 and 0.79 and root mean square errors of 3.8 and 2.6 L for males and females, respectively; CV: 8%) and tended to underpredict TBW in black males (2.0 L) and females (1.4 L) and to overpredict TBW in white males (0.5 L) and females (0.3 L). The race-combined FFM prediction equations contained the same independent variables (R(2) = 0.90 and 0.83 and root mean square errors of 3.9 and 2.9 kg for males and females, respectively; CV: approximately 6%) and tended to underpredict FFM in black males (2.1 kg) and females (1.6 kg) and to overpredict FFM in white males (0.4 kg) and females (0.3 kg). CONCLUSION: These equations have excellent precision and are recommended for use in epidemiologic studies to describe normal levels of body composition.     

Estimation of total-body and limb muscle mass in hemodialysis patients by using multifrequency bioimpedance spectroscopy

BACKGROUND: Skeletal muscle mass can be measured noninvasively with magnetic resonance imaging (MRI), but this is time-consuming and expensive. OBJECTIVE: We evaluated the use of multifrequency bioimpedance spectroscopy (BIS) measurements of intracellular volume (ICV) to model total-body skeletal muscle mass (TBMM) and limb skeletal muscle mass in hemodialysis patients. DESIGN: TBMM was measured by MRI in 20 male and 18 female hemodialysis patients with a median (range) age of 54 y (33-73 y), weight of 78.9 kg (43.2-120 kg), and body mass index (BMI; in kg/m2) of 27.3 (19.4-46.6). We measured total body water (TBW) by using D2O dilution, extracellular volume (ECV) as bromide space, and ICV as TBW minus bromide space. Total body potassium (TBK) measured as 40K was used as an independent model of TBMM. BIS was used to measure whole-body TBW (ankle to wrist) and TBW in the arms and legs. BIS-estimated ICV was used to construct models to calculate limb muscle mass and TBMM. The latter was compared with models derived from isotopic methods. RESULTS: BIS yielded a model for TBMM [TBMM = 9.52 + 0.331 x ICV + 2.77 (male) + 0.180 x weight (kg) - 0.133 x age] (R2 = 0.937, P < 0.0001) as precise as TBK-measured TBMM [TBMM = 1.29 + 0.00453 x TBK (mEq) + 1.46 (male) + 0.144 x weight (kg) - 0.0565 x age] (R2 = 0.930, P < 0.0001) or isotopic methods. BIS models were also developed for measuring leg and arm muscle mass. CONCLUSION: BIS provides an estimate of TBMM that correlates well with isotopic methods in approximating values obtained by MRI and can be used to estimate limb muscle mass.     

Evaluation of a foot-to-foot impedance meter measuring extracellular fluid volume in addition to fat-free mass and fat tissue mass

OBJECTIVES: The first objective was to compare the accuracy of a foot-to-foot impedance meter with a multifrequency bioimpedance for measurements of fat-free mass (FFM) and fat mass (FM) using dual energy X-ray absorptiometry (DXA) as reference. The second objective was to validate measurements of extracellular water resistance and volume by the foot-to-foot impedance meter, using multifrequency bioimpedance as reference. METHODS: This investigation was carried out in 60 volunteers 18 to 71 y of age. Impedance meters were a Tefal Bodymaster Vision (foot-to-foot) that featured a square wave signal and a Xitron Hydra 4200 (5 to 1000 kHz) by using the bioimpedance spectroscopic method. RESULTS: Bland-Altman tests showed that FFM differences between Tefal and DXA data were 1.98 +/- 3.09 kg in men and -0.08+/-2.98 kg in women. Total body water was measured by the Xitron, and FFM as measured with the Xitron was calculated as total body water divided by 0.732. Mean differences between Xitron-measured and DXA-measured FFM were 2.37+/-3.03 kg for men and 2.84+/-2.40 kg for women, indicating a systematic underestimation by the Xitron of intracellular volume. Extracellular water resistances measured by Tefal were in good agreement with those measured by Xitron with electrodes pasted under the subject's feet (mean difference 8.5+/-31 Omega). Extracellular water volumes were calculated from Tefal-measured extracellular water resistances by using a modified bioimpedance spectroscopic method and differed from those measured with Xitron by-0.03+/-0.66 L. CONCLUSION: Limits of agreement with DXA-measured FFM produced by the foot-to-foot impedance meter tested are too large for clinical measurements in individuals, but they are sufficient to assess FFM in groups of subjects and for home use. Our prototype was also capable of estimating extracellular water volume with a similar accuracy as multifrequency bioimpedance in normal subjects.     

Body-water compartments measured by bio-electrical impedance spectroscopy in patients with chronic obstructive pulmonary disease

It was previously demonstrated that single frequency bio-electrical impedance (BIA) measurement at 50 kHz is a useful method to assess total body water (TBW) in patients with chronic obstructive pulmonary disease (COPD). In the present study it was examined whether bio-electrical impedance spectroscopy (BIS) could predict extracellular water (ECW) and improve the prediction of TBW in these patients. TBW and ECW (corrected bromide space) were measured by deuterium and bromide dilution. In 37 COPD patients prediction equations were obtained using BIS (5-500 kHz) measurements, and these were cross validated in a second group of 40 COPD patients. All patients were in a clinically stable condition. TBW predicted by BIS was not significantly different from actual TBW and demonstrated a comparable standard error of estimate (SEE) as found previously in healthy subjects (male symbol correlation coefficient: r = 0.88, SEE: 2.3 L, female symbol r = 0.85, SEE: 2.9 L). Predicted ECW using BIS-measurements was not significantly different from measured ECW (male symbol r = 0.75, SEE: 1.4 L, female symbol r = 0.73, SEE: 1.2 L), but the error in the prediction was relatively large and the correlation between predicted and actual ECW relatively low compared to most studies in healthy subjects. Predicted TBW using BIS was comparable to actual TBW, but presented no improvement of the prediction of TBW using BIA at 50 kHz and a patient specific regression equation. The error of the prediction of ECW by BIS limits the ability to predict fluid shifts in individual patients with clinically stable COPD.