Equations For Total Body Water Research Articles

Body composition among Malawian young adolescents: Cross-validating predictive equations for bioelectric impedance analysis using deuterium dilution method.

Body composition can be measured by several methods, each with specific benefits and disadvantages. Bioelectric impedance offers a favorable balance between accuracy, cost and ease of measurement in a range of settings. In this method, bioelectric measurements are converted to body composition measurements by prediction equations specific to age, population and bioimpedance device. Few prediction equations exist for populations in low-resource settings. We formed a prediction equation for total body water in Malawian adolescents using deuterium dilution as reference. We studied 86 boys and 92 girls participating in the 11-14-year follow-up of the Lungwena Antenatal Intervention Study, a randomized trial of presumptive infection treatment among pregnant women. We measured body composition by Seca m515 bioimpedance analyser. Participants ingested a weight-standardized dose of deuterium oxide, after which we collected saliva at baseline, at 3 and 4 h post-ingestion, measured deuterium concentration using Fourier-transform infrared spectroscopy and calculated total body water. We formed predictive equations for total body water using anthropometrics plus resistance and reactance at a range of frequencies, applying multiple regression and repeated cross-validation in model building and in prediction error estimation. The best predictive model for percentage total body water (TBW %) was 100*(1.11373 + 0.0037049*height (cm)2/resistance(Ω) at 50 kHz- 0.25778*height(m)- 0.01812*BMI(kg/m2)- 0.02614*female sex). Calculation of absolute TBW (kg) by multiplying TBW (%) with body weight had better predictive power than a model directly constructed to predict absolute total body water (kg). This model explained 96.4% of variance in TBW (kg) and had a mean prediction error of 0.691 kg. Mean bias was 0.01 kg (95% limits of agreement -1.34, 1.36) for boys and -0.01 kg (1.41, 1.38) for girls. Our equation provides an accurate, cost-effective and participant-friendly body composition prediction method among adolescents in clinic-based field studies in rural Africa, where electricity is available.

Forensic alcohol calculations in transgender individuals undergoing gender-affirming hormonal treatment.

There are an increasing number of individuals undergoing gender‐affirming hormonal treatment (GAHT) to treat gender dysphoria. Current forensic alcohol calculations require knowledge of the sex of the individual, but this may disadvantage trans people as research has demonstrated that there are physiological changes in individuals who are undergoing GAHT. Using previously published studies on total body water (TBW) in cis individuals, and the known changes in lean body mass and hematocrit in trans individuals, it is possible to estimate TBW in trans individuals and compare them to those cis equation estimations. When using these revised rubrics, we determined that for trans women the use of the cis male anthropometric TBW equation only gives a small underestimation of TBW (0.9%) compared to the underestimation of TBW using the cis female TBW equation (−17.7%). For trans men, the use of the cis female TBW equation gives the largest disadvantage, underestimating TBW by −10.8% compared to the cis male TBW equation, that overestimates TBW by 6.6%. For this reason, we recommend that if the sex at birth of an individual is not known or disclosed, any forensic alcohol calculations in a forensic alcohol reports are made assuming that the gender declared by the individual is their sex at birth. Further research to develop validated anthropometric TBW equations are urgently needed as to not disadvantage trans people when forensic alcohol calculations are carried out.

Validation and predicting total body water in people with spinal cord injury using bioelectrical impedance analysis

The purpose of this study was validation of predictive equations for total body water (TBW) in people with spinal cord injury (SCI) compared to healthy subjects (HS) using bioelectrical impedance analysis (BIA). The method used was sample size of 104 (52 each group) with 41 males in SCI, 39 in HS, 11 females in SCI, and 13 in HS. A T-test was applied to statistical analysis between groups. The results showed significant differences between groups of gender, with p-value < P 0.0013, the difference (4.6115), with a 95%CI (1.8480 to 7.3750), and SE (1.3932). The SCI group noted a difference within BIA and formula calculations. In conclusion, we found the current equations inaccurate in SCI society and recommended BIA as non-invasive, speedy, portable, accessible, and cost-effective.

Generalized bioelectric impedance-based equations underestimate body fluids in athletes.

The current study aimed: (i) to external validate total body water (TBW) and extracellular water (ECW) derived from athlete and non‐athlete predictive equations using radioisotope dilution techniques as a reference criterion in male and female athletes; (ii) in a larger sample, to determine the agreement between specific and generalized equations when estimating body fluids in male and female athletes practicing different sports. A total of 1371 athletes (men: n = 921, age 23.9 ± 1.4 y; women: n = 450, age 27.3 ± 6.8 y) participated in this study. All athletes underwent bioelectrical impedance analyses, while TBW and ECW were assessed with dilution techniques in a subgroup of 185 participants (men: n = 132, age 21.7 ± 5.1 y; women: n = 53, age 20.3 ± 4.5 y). Two specific and eight generalized predictive equations were tested. Compared to the criterion methods, no mean bias was observed using the athlete‐specific equations for TBW and ECW (−0.32 to 0.05, p > 0.05) and the coefficient of determination ranged from R 2 = 0.83 to 0.94. The majority of the generalized predictive equations underestimated TBW and ECW (p < 0.05); R 2 ranged from 0.66 to 0.89. In the larger sample, all the generalized equations showed lower TBW and ECW values (ranging from −6.58 to −0.19, p < 0.05) than specific predictive equations; except for TBW in female power/velocity (one equation) athletes and team sport (two equations). The use of generalized BIA‐based equations leads to an underestimation of TBW, and ECW compared to athlete‐specific predictive equations. Additionally, the larger sample indicates that generalized equations overall provided lower TBW and ECW compared to the athlete‐specific equations.

Bioelectrical impedance analysis, hydrometry and hydrodensitometry for body composition assessment in adult Colombian women

Bioelectrical impedance analysis (BIA) is a noninvasive method for assessment of body composition with better accuracy, and less inter-observer error than anthropometry. Despite these advantages, reported BIA equations may not be suitable for populations other than where they were developed. The aim of this study was to develop equations for single-frequency (SF) BIA and bioelectrical impedance spectroscopy (BIS) using a three compartment (3C) model as the criterion method to predict total body water (TBW) and fat-free mass (FFM) in South-American adult women. A cross-sectional observational study was conducted using a convenience sample (n=40). SF-BIA and BIS prediction equations were developed using forward-stepwise multiple regression with TBW by D2O and FFM by 3C model as dependent variables; and weight, resistance and impedance index (stature2/resistance) as independent variables. A cross-validation was conducted in a randomly split subsample (n=20). Four final equations were developed. There were no differences between SF-BIA and BIS equations for TBW (p=0.68) and FFM (p=0.66). The cross-validation showed a strong association and broadly meets the limits of agreement with the 3C reference method. The equations have an excellent goodness-of-fit to predict TBW and FFM. Validation of these equations in populations of different ages and ethnicities is warranted.

Development and validation of impedance-based equations for the prediction of total body water and fat free mass in children aged 8 to 11 years

Introduction et but de l’etude Accuracy of the impedance analysis depends on population-specific prediction equations. The aim of this study was to propose new prediction equations to estimate body composition using impedance analysis for healthy Tunisian children and validate them using the deuterium oxide dilution (D2O) technique. Materiel et methodes The body composition was estimated by the Tanita impedance analyzer. The validity of this system was investigated in 134 school children aged between 8 and 11 years. The validity of other published equations was also tested in our sample. Total body water (TBW) and Fat Free Mass (FFM) were determined using the D 2O technique. Participants were divided equally into development (n = 67) and validation groups (n = 67) to develop prediction equation using linear regression models. Resultats et analyse statistique The comparison between body composition obtained by Tanita system and by D2O technique illustrated a significant difference (P O technique, the impedance analysis underestimates fat mass and overestimates FFM and TBW. The prediction equations for TBW and FFM were developed with sex, age, weight and resistance index as possible predictor variables . The selected equations presented the highest adjusted coefficient of determination (R 2), the lowest standard error of the estimate (SEE) value and the lowest P values. The pure error was 1.263 for the TBW equation and 1.646 for the FFM. The Bland Altman plot illustrated the good level of concordance between the TBW and FFM predicted by the new equations and measured by isotope dilution. Conclusion Our study provides valid prediction equations for estimation of TBW, FFM from impedance analysis measures for Tunisian children. These equations are applicable to children aged between 8 and 11 years.

Prediction equations for body composition of children and adolescents aged 8–19 years in Uganda using deuterium dilution as the reference technique

Body composition is important as a marker of both current and future health status. Bioelectrical impedance analysis (BIA) is a simple and accurate method for estimating body composition in field, clinical and research settings, if standard protocol procedures are followed. However, BIA requires population-specific equations since applicability of existing equations to diverse populations has been questioned. This study aimed to derive predictive equations for Total Body Water (TBW), Fat Free Mass (FFM) and Fat Mass (FM) determinations with BIA and anthropometric measurements in a population of children and adolescents aged 8-19 years in Uganda. A cross-sectional study was conducted among 203 children and adolescents aged 8-19 years attending schools in Kampala district (also referred to as Kampala city since the city is conterminous with the district), Uganda through a two-stage cluster sample design. Deuterium dilution method (DDM) was used as the reference measure while BIA and anthropometric measures were used to create the new body composition prediction equations through multivariate regression. The new prediction equations explained 88%, 87% and 71% of the variance in TBW, FFM % and of FM respectively with no statistical shrinkage upon cross-validation. The linear regression models proposed in this study were well adjusted with respect to TBW, FFM and FM. Log of TBW obtained by DDM=0.0129×Impedance index+0.0055×Age+0.0049 Waist Circumference+0.1219Ht2+2.0388. Log of FFM obtained by DDM=0.0197×FFM obtained by BIA - 0.0181 sex code - 0.00055×Impedance+3.1761. Log of FM obtained by DDM=0.0634×FM obtained by BIA - 0.1881 sex code+0.0252×Weight+0.5273. The use of these equations for more accurate body composition assessment may facilitate identification of effective intervention strategies to prevent or combat overweight and obesity among children and adolescents. They may also assist in treatment of conditions where more accurate information on body composition measures is required.

Development and validation of impedance-based equations for the prediction of total body water and fat-free mass in children aged 8–11 years

Accuracy of impedance analysis depends on population-specific prediction equations. The aim of this study was to propose new prediction equations to estimate body composition using impedance analysis for healthy Tunisian children and validate them using the deuterium oxide dilution (D2O) technique. Body composition was estimated by the Tanita impedance analyzer. The validity of this system was investigated in 134 school children aged between 8 and 11 years. The validity of other published equations was also tested in our sample. Total body water (TBW) and Fat-Free Mass (FFM) were determined using the D2O technique. Participants were divided equally into development (n=67) and validation groups (n=67) to develop prediction equation using linear regression models. The comparison between body composition obtained by Tanita system and by D2O technique illustrated a significant difference (p<0.01). Compared to D2O technique, Tanita impedance analysis underestimates fat mass and overestimates FFM and TBW. The prediction equations for TBW and FFM were developed with sex, age, weight and resistance index as possible predictor variables. The selected equations presented the highest adjusted coefficient of determination (R2), the lowest standard error of the estimate (SEE) value and the lowest p-values. The pure error was 1.263 for the TBW equation and 1.646 for the FFM. The Bland Altman plot illustrated the good level of concordance between the TBW and FFM predicted by the new equations and measured by isotope dilution. Our study provides valid prediction equations for estimation of TBW, FFM from impedance analysis measures for Tunisian children. These equations are applicable to children aged between 8 and 11 years.

Validation of anthropometric and bioelectrical impedance analysis (BIA) equations to predict total body water in a group of Cameroonian preschool children using deuterium dilution method

BackgroundLittle information is available on the validity of anthropometry or impedance-based equations for prediction of total body water (TBW) in African children. This study was designed to validate and develop equations to predict total body water in Cameroonian children.MethodsTBW was measured by deuterium dilution in 102 children between 24 and 60 months of age and compared with the ones predicted by 5 anthropometric and 7 BIA equations. Multiple linear regression analysis was used to develop prediction equations for TBW from anthropometric parameters.ResultsUnacceptable discrepancies in the estimates of TBW at individual level were noted with all the equations tested. The following new anthropometry and BIA equations for the estimation of TBW were respectively developed: TBW = 6.488 + 0.434 × sex − 0.039 × age + 0.670 × weight − 0.081 × MUAC (cm) − 0.372 × BMI (adjusted R2 = 0.71, RMSE = 3.6), and TBW = −6.206 + 0.0037 × height2/Z − 0.041 × age + 0.265 × weight + 0.1214 × height (adjusted R2 = 0.68, RMSE = 1.4). The cross-validation procedures revealed that the predicted values of TBW compared with measured values are accurate at a group level.ConclusionThe current published anthropometric and BIA equations are invalid for the estimation of TBW in Cameroonian preschool children. The newly developed anthropometry or BIA prediction equations are valid for use in Cameroonian children aged 24–60 months.

Development and validation of bioelectrical impedance analysis equations for predicting total body water and fat-free mass in North-African adults

Accuracy of the bioelectrical impedance analysis (BIA) depends on population-specific prediction equations. The aim of our study was to develop prediction equations for assessing total body water (TBW) and fat-free mass (FFM) in healthy North-African adults. In all, 250 participants (194 women, 56 men) aged 18-64 years were included in the analysis. BIA variables were measured by a tetra-polar device. TBW and FFM were assessed by the dilution of deuterium (D2O). The participants were sorted by gender and randomly split into development and validation subgroups. The validity of other published equations was also tested using Bland and Altman procedure, proportional bias and pure error. The prediction equations derived were: TBW (l)=5.68+0.267 height(2)/resistance+4.42 sex (male=1, female=0) + 0.225 weight-0.052 age (R(2)=0.92, root mean square error (RMSE)=1.75 l, RMSE%=5.65); and FFM (kg)=7.47 + 0.366 height(2)/resistance+6.04 sex + 0.306 weight-0.063 age (R(2)=0.92, RMSE=2.38 kg, RMSE%=5.61). The new equations provided nonsignificant proportional bias values, and better agreement than other tested equations. Bias and pure error values were 0.36 and 1.88 l for men and 0.00 and 1.82 l for women, for TBW equation. For FFM equation, bias values were 0.43 and -0.04 kg, and pure errors were 2.57 and 2.46 kg for men and women, respectively. The new prediction equations provide reliable estimates of TBW and FFM in North-African adults and are recommended for use in these populations.

Body composition in urban South Asian women; development of a bioelectrical impedance analysis prediction equation

Background: Assessment of body composition plays a significant role in combating chronic disease among South Asians. Accurate assessment of body composition by bioelectrical impedance analysis (BIA) requires population-specific equations which are currently unavailable for urban South Asian women.Aim: To assess validity of direct BIA assessment and selected equations for prediction of total body water (TBW), against Deuterium (2H2O) dilution and develop and validate a population-specific TBW equation for urban South Asian women.Subjects and method: Data of 80 urban Sri Lankan women (30–45 years) were used for this analysis. Body composition was assessed by 2H2O dilution (reference) and BIA. Available BIA equations were assessed for validity. A new TBW equation was generated and validated.Results: Direct BIA measurements and other equations did not meet validation criteria in predicting TBW. TBW by the new equation (TBW = 3.443 + 0.342 × (height2/impedance) + 0.176 × weight) correlated (p < 0.001) with TBW by reference method. TBW using the new equation was not significantly different (25.30 ± 2.4 kg) from the reference (25.32 ± 2.7 kg).Conclusion: Direct use of TBW by instrument and existing equations are less suitable for this population. The new TBW equation is suitable for body composition assessment in urban South Asian women.

Bioelectrical impedance analysis for assessment of fluid status and body composition in neonates—the good, the bad and the unknown

There is a critical need for improved technologies to monitor fluid balance and body composition in neonates, particularly those receiving intensive care. Bioelectrical impedance analysis meets many of the criteria required in this environment and appears to be effective for monitoring physiological trends. The literature regarding the use of bioelectrical impedance in neonates was reviewed. It was found that prediction equations for total body water, extracellular water and fat-free mass have been developed, but many require further testing and validation in larger cohorts. Alternative approaches based on Hanai mixture theory or vector analysis are in the early stages of investigation in neonates. Further research is required into electrode positioning, bioimpedance spectroscopy and Cole analysis in order to realise the full potential of this technology.

Development of predictive equations for total body water using the deuterium-dilution method as the gold standard in a population of asymptomatic HIV-positive Zulu women in South Africa

Objectives: The study aimed to derive predictive equations for total body water determinations with bioelectrical impedance and anthropometric measurements in a population of asymptomatic human immunodeficiency virus (HIV) -positive Zulu women.Design: Cross-sectional data from within an ongoing prospective study that observed the effect of infant feeding mode on maternal and child health in a cohort of asymptomatic HIV-positive women were used for this objective.Setting: A community health centre in Durban.Subjects: Asymptomatic HIV-infected women who were not eligible for antiretroviral therapy. They were resident in the area and were of Zulu ethnicity.Outcome measures: Development of predictive equations for total body water.Results: Success was achieved in developing predictive equations for total body water using bioelectrical impedance analysis and anthropometric measurements that were specific to the HIV-positive female Zulu population. These equations were developed using the total body water that was obtained from deuterium-dilution method as a gold standard.Conclusion: These predictive equations are likely to be more valid for the HIV-positive female African populations of similar build than the current predictive equations that derive from the Western population.

Bioelectrical impedance analysis determination of water content and distribution in the horse

A horse’s hydration status is critical to its health. The accurate and quantitative determination of it has been problematic because of size, length and density of hair, and uneven topography. The objective of this study was to validate a bioelectrical impedance analysis (BIA) method for objectively quantifying hydration status. Monofrequency BIA values and simple biometric measurements were used to construct predictive equations for total body water, plasma, extracellular, and intra-cellular fluid volumes. These predictive equations were correlated with standard body fluid dilution reference methods. The result was an accuracy of ±0.64% for total body water, ±0.17% for plasma volume, ±1.91% for extra-cellular fluid, and ±0.57% for intra-cellular fluid compartments. Less than 5 min was required for all of the measurements and determinations. Therefore, it appears that an accurate measurement of body fluid distribution can be performed on horses using a fast, easy, non-invasive, inexpensive BIA method.

Total body water changes after an exercise intervention tracked using bioimpedance spectroscopy: A deuterium oxide comparison

Bioimpedance spectroscopy (BIS) for the estimation of total body water (TBW) has advantages over isotope dilution techniques, including cost, portability, and ease of use. The aim of the current study was to determine the validity of a BIS device (Imp SFB7) for tracking changes in overfat and obese individuals. Sixty overfat and obese men and women (27+/-8 yr, 33.41+/-3.81%fat) participated in the study. TBW was estimated using BIS and deuterium oxide (D(2)O) before and after the ten-week intervention. Pre-and post-intervention BIS TBW estimations errors increased as body mass index (BMI), fat mass (FM), and fat-free mass (FFM) increased (p<0.05). Delta values were more accurate than pre- and post-TBW estimations (total error=1.45 L). Age significantly influenced pre- and post-TBW errors (p<0.05). Therefore, a regression equation was developed to correct for the pre- and post-BIS-estimated TBW errors: D(2)O TBW=11.478+0.743(BIS TBW)-2.429(Gender), (Men=1, Women=2). BIS can be considered an accurate tool for tracking changes in TBW regardless of variations in BMI, FM, FFM, or age in both overfat and obese men and women (BMI>24). Employing a BIS TBW equation is suggested over the development of resistivity coefficients based on BMI, FM, FFM or age.

Validación de ecuaciones antropométricas para evaluar composición corporal en niños preescolares chilenos

Validated equations to measure body composition in Chilean preschool children are lacking, since the only international equation available was developed in obese, and undernourished Caucasian children. Due to the increase in overweight and obesity in Chile, it is essential to have simple and reliable instruments to assess children.To design and validate anthropometric equations to estimate body fat (BF) and total body water (TBW) to be applicable in children aged 3 to 5 years, using deuterated water dilution as a reference method.Weight, height, circumferences and skinfold thickness were evaluated in 238 children aged 3 to 5 years, attending Junta Nacional de Jardines Infantiles (JUNJI). Several equations were developed using multiple regression models to estimate body water and fat. The proposed equations were validated against a sample of 77 children previously evaluated, using Bland and Alunan agreement analysis, that compares average differences of both methods with the average of predicted and estimated values.New equations for TBW and BF were obtained, accounting for 86% and 72% in estimated variability. The agreement analysis showed a mean difference 0.001 +/- 0.32 and 0.07 +/- 0.56 kg, for TBW and BF, respectively, confirming the validity of the equations.The new validated equations in Chilean children aged 3 to 5 years, have an adequate and predictive capacity, especially useful for evaluating TBW and BF change in cohorts.

Validation of equations to assess body composition using anthropometric data in Chilean preschool children

Validated equations to measure body composition in Chilean preschool children are lacking, since the only international equation available was developed in obese, and undernourished Caucasian children. Due to the increase in overweight and obesity in Chile, it is essential to have simple and reliable instruments to assess children. To design and validate anthropometric equations to estimate body fat (BF) and total body water (TBW) to be applicable in children aged 3 to 5 years, using deuterated water dilution as a reference method. Weight, height, circumferences and skinfold thickness were evaluated in 238 children aged 3 to 5 years, attending Junta Nacional de Jardines Infantiles (JUNJI). Several equations were developed using multiple regression models to estimate body water and fat. The proposed equations were validated against a sample of 77 children previously evaluated, using Bland and Alunan agreement analysis, that compares average differences of both methods with the average of predicted and estimated values. New equations for TBW and BF were obtained, accounting for 86% and 72% in estimated variability. The agreement analysis showed a mean difference 0.001 +/- 0.32 and 0.07 +/- 0.56 kg, for TBW and BF, respectively, confirming the validity of the equations. The new validated equations in Chilean children aged 3 to 5 years, have an adequate and predictive capacity, especially useful for evaluating TBW and BF change in cohorts.

Bioelectric impedance vector distribution in peritoneal dialysis patients with different hydration status

In continuous ambulatory peritoneal dialysis (CAPD), total body water (TBW) is estimated by functions of body weight, and by equations of bioelectric impedance analysis (BIA). These procedures may be biased with abnormal tissue hydration. We validated vector BIA (BIVA) patterns of hydration in CAPD patients, based on direct measurements of resistance (R) and reactance (Xc) (RXc graph) without knowledge of the body weight. Cross-sectional study in 200 adult CAPD patients from two groups: 149 patients (77 males and 72 females) without edema (BMI 24.3 kg/m2), and 51 (29 males and 22 females) with pitting edema (BMI 24.6 kg/m2). Single frequency (50 kHz), whole-body impedance vector was measured with both empty and filled peritoneal cavity. Vector distribution was compared with that from 726 healthy subjects, 1116 hemodialysis patients, and 50 nephrotic patients, all with a same BMI. The performance of BIVA was compared with indications of four anthropometry and four conventional BIA equations for TBW. TBW estimates from anthropometry (Watson, Hume and Weyers, Chertow, and Johansson formulas) were misleading, indicating the same hydration in edema. TBW estimates from BIA equations indicated a 10% excess TBW in edema. BIVA were very sensitive to fluid overload, as both R (by 10%) and Xc (by 40%) were reduced in patients with edema (regardless of peritoneal filling). The vector distribution of individual CAPD patients without edema was superposable to that of the healthy, gender-specific, reference population (50%, 75%, and 95% tolerance ellipses, RXc graph) and close to the hemodialysis, presession distribution. Vectors from patients with edema were displaced downward on the RXc graph, out of the 75% ellipse (88% sensitivity and 87% specificity), and close to vectors from nephrotic patients. CAPD prescription would keep or bring vectors of patients back into the 75% reference ellipse (border for progression from latent to apparent overhydration across the lower pole) regardless of body weight. Whether CAPD patients with vector within the target ellipse have better outcome needs longitudinal evaluation.

Body composition of children in south-western Nigeria: validation of bio-electrical impedance analysis.

Bio-electrical impedance analysis (BIA) is a non-invasive method of estimating body composition and has the potential to be useful in clinics and for nutrition and health-related research in Africa. We sought to validate BIA for use among a Yoruba population in south-western Nigeria and to use BIA to assess the body composition of a healthy cohort of children. Total body water (TBW) was measured in 92 individuals (53 adults and 39 children) using deuterium dilution; height, weight and resistance were measured by BIA. Multiple regression analysis was used to develop prediction equations for TBW among children only or among all participants. Independent covariates tested in the regression models included the impedance index (height(2)/resistance), weight, age and gender with TBW as the dependent variable. Depending on the model used, between 97% (root MSE=0.7 kg ) and 99% (root MSE=0.7 kg) of the variance observed in TBW could be explained by the impedance index, weight and/or gender; age, however, was not significant in any model. In a separate cohort of 69 children, 5-8 years old, anthropometrics were measured and TBW was estimated using the developed equations. Body composition data are presented by gender and age group. BIA was validated for use among Nigerian children and adults and provides a potentially important tool for research.

Bioelectrical impedance analysis models for prediction of total body water and fat-free mass in healthy and HIV-infected children and adolescents , ,

Bioelectrical impedance analysis (BIA) is an attractive method of measuring pediatric body composition in the field, but the applicability of existing equations to diverse populations has been questioned. The objectives were to evaluate the performance of 13 published pediatric BIA-based predictive equations for total body water (TBW) and fat-free mass (FFM) and to refit the best-performing models. We used TBW by deuterium dilution, FFM by dual-energy X-ray absorptiometry, and BIA-derived variables to evaluate BIA models in a cross-sectional study of 1291 pediatric subjects aged 4-18 y, from several ethnic backgrounds, including 54 children with HIV infection and 627 females. The best-performing models were refitted according to criterion values from this population, cross-validated, and assessed for performance. Additional variables were added to improve the predictive accuracy of the equations. The correlation between predicted and criterion values was high for all models tested, but bias and precision improved with the refitted models. The 95% limits of agreement between predicted and criterion values were 16% and 11% for TBW and FFM, respectively. Bias was significant for some subgroups, and there was greater loss of precision in specific age groups and pubertal stages. The models with additional variables eliminated bias, but the limits of agreement and the loss of precision persisted. This study confirms that BIA prediction models may not be appropriate for individual evaluation but are suitable for population studies. Additional variables may be necessary to eliminate bias for specific subgroups.