Prediction Of Total Body Water Research Articles

Anthropometry-Based Prediction Equation of Body Composition in a Population Aged 12–88 Years

BackgroundDirect anthropometric measurements to assess body composition have limited precision and/or specificity. ObjectivesThe study aimed to develop a prediction equation based on anthropometric measurements for estimating total body water (TBW) in a healthy population. MethodsTBW was assessed using the deuterium dilution method in 398 Moroccan participants (235 women and 163 men) aged 11.6–88 y, then compared to the estimations made by previously published anthropometric equations. By sex, participants were randomly assigned into development (n = 199) and validation subgroups (n = 199). A new anthropometric equation was developed in the development subgroup from data obtained on body volume (BV), weight, and sex, where the BV was calculated from participants’ height. Then the equation was validated in the validation subgroup using the Bland and Altman procedure, bias, and pure error. External validation was performed using a sample from Tunisia (n = 220, 51.8% female, 18–65 y). ResultsBias in predicting TBW showed unacceptable value for all previously published equations as it was significantly overestimated. The following new equation using anthropometric measurements [TBW (kg) = –5.249 + 107.502 BV (L) + 0.289 weight (kg) + 2.015 sex (male: 1, female: 0); (R2 = 0.91, RMSE = 1.885 kg)] was developed, and its internal validation was confirmed. The generated bias and pure error values were 0.047 kg (95% CI: –0.235, 0.330) and 2.02 kg (95% CI: 1.73, 2.31), respectively. The external validation of the new TBW prediction equation on a Tunisian sample showed a bias and pure error values of 0.07 kg (95% CI: –0.289, 0.429) and 2.36 kg, respectively. ConclusionsThe results indicate that the new anthropometric-based prediction equation provides a good estimation of TBW and other body composition compartments. It could be recommended as an alternative method to assess body composition for epidemiological and clinical studies.

Use of bioelectrical impedance spectroscopy to provide a measure of body composition in sows

The ability to accurately estimate fat mass and fat-free mass (FFM) has the potential to improve the way in which sow body condition can be managed in a breeding herd. Bioelectrical impedance spectroscopy (BIS) has been evaluated as a practical technique for assessment of body composition in several livestock species, but similar work is lacking in sows. Bioelectrical impedance uses population-specific algorithms that require values for the apparent resistivities of body fluids and body proportion factors. This study comprised three major aims: (i) to derive apparent resistivity coefficients for extracellular water (ECW) and intracellular water (ICW) required for validation of BIS predictions of total body water (TBW) in live sows against standard reference tracer dilution methods; (ii) to develop predictions of TBW to body composition prediction algorithms, namely FFM, by developing a body geometry correction factor (Kb) and (iii) to compare the BIS predictions of FFM against existing impedance predictors and published prediction equations for use in sows, based on physical measurements of back-fat depth and BW (P2-based predictors). Whole body impedance measurements and the determination of TBW by deuterium dilution and ECW by bromide dilution were performed on 40 Large White x Landrace sows. Mean apparent resistivity coefficients of body fluids were 431.1 Ω.cm for ECW and 1827.8 Ω.cm for ICW. Using these coefficients, TBW and ECW were over-estimated by 6.5 and 3.3%, respectively, compared to measured reference values, although these differences were not statistically different (P > 0.05). Mean Kb was 1.09 ± 0.14. Fat-free mass predictions were 194.9 kg, which equates to 60.9% of total sow weight, and 183.0 kg for BIS and the deuterium dilution method, respectively. Mean differences between the predicted and measured FFM values ranged from −8.2 to 32.7%, but were not statistically different (P > 0.05). Method validation (leave-one-out procedure) revealed that mean differences between predicted and measured values were not statistically significant (P > 0.05). Of the impedance-based predictors, equivalence testing revealed that BIS displayed the lowest test bias of 11.9 kg (8.2%), although the P2-based prediction equations exhibited the lowest bias and percentage equivalence, with narrow limits of agreement. Results indicate although differences between mean predicted and measured values were not significantly different, relatively wide limits of agreement suggest BIS as an impractical option for assessing body composition in individual sows compared to the use of existing prediction equations based on BW and back fat.

Total body water is the preferred method to use in forensic blood-alcohol calculations rather than ethanol’s volume of distribution

During the prosecution and defence of drink-driving cases, forensic practitioners are often required to engage in various blood-alcohol calculations, such as whether or not the statutory limit was exceeded (e.g. 80mg/100mL, 0.08g/100mL or 0.80g/L). For this purpose, most forensic scientists utilize the Widmark equation, or some modification thereof, to calculate a person’s blood alcohol concentration (BAC) based on information about the amount of ethanol consumed and the pattern of drinking. This equation comes in two main forms; one of which incorporates the apparent volume of distribution of ethanol (V) and the other a person’s total body water (TBW). In this study, we utilised two independent data sets, one involving the determination of V for ethanol in 173 men and 63 women, and the other TBW determined for 582 men and 884 women. Those subjects included in the TBW group represented various racial groups (Caucasians, African Americans, Hispanics, Asians and Puerto Ricans), with body mass index (BMI) ranging from 17 to 80kg/m2. Both versions of the Widmark equation were evaluated in relation to their accuracy and precision in predicting TBW and/or V using the two most common anthropometric equations; those of Watson et al. and Forrest. Both anthropometric equations exhibited good accuracy (<4.3%) for the prediction of both TBW and V. However, the root mean square error was lower TBW was used for prediction (9.09–12.84%) rather than V (11.72–15.08%). Overall, this study has demonstrated (a) that blood-alcohol calculations are more reliable using TBW rather than V (b) that both equations (Watson et al. and Forrest) are applicable to ethnic groups other than Caucasians and (c) the Forrest equation predicts TBW in men and women with BMI from 17 to 35kg/m2 and that the Watson et al. equation works for those with more extreme BMI; females (17–80kg/m2) and males (17–67kg/m2).

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.

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.

The Combyn™ ECG: Adding haemodynamic and fluid leads for the ECG. Part II: Prediction of total body water (TBW), extracellular fluid (ECF), ECF overload, fat mass (FM) and “dry” appendicular muscle mass (AppMM)

Simultaneous with a 12 channel ECG, body composition was analysed by segmental multi-frequency impedance analysis in 101 healthy subjects and in 118 patients with chronic heart failure (CHF, n= 40), chronic renal failure with haemodialysis (HD, n= 20), and miscellaneous internal diseases (n= 58). Whole body DXA and sodium bromide dilution were used as reference methods for total body water (TBW), extracellular fluid (ECF), appendicular muscle mass (AppMM) and fat mass (FM). Empirical prediction equations were developed in a randomized evaluation sample and then evaluated in unknowns. TBW, ECF, AppMM and FM could be predicted with regression coefficients of 0.96, 0.90, 0.95 and 0.93, respectively, all with p< 0.001. Only segmental impedances and height, but not age, sex, weight and BMI contributed to the prediction of water compartments. About half the patients with CHF and half of those on HD showed increased ECF/ICF ratio in relation to % FM at the legs but not at the thorax. The predicted AppMM was additionally corrected for increased ECF to determine “dry AppMM”, which is markedly lower than the misleading reference DXA.This methodology shows promise as a combination of routine ECG with measurement of body composition, assessment of sarcopenia and detection of overhydration.

Resonant cavity perturbation: a promising new method for the assessment of total body water in children

The accurate measurement of total body water (TBW) in children has important clinical and nutritional applications. Resonant cavity perturbation (RCP) is a new method for estimating TBW. This method measures the dielectric properties of the body which are related to body water. For RCP measurements, each subject lay supine on a bed inside a screened room which acts as a resonant cavity. A network analyser measures the frequencies of two low-order cavity resonances of the room, with electric-field vectors that were respectively vertical and horizontal, the resonant frequency shifts relative to the empty room are then derived. These frequency shifts correlates with TBW. The aims of this present study were to (a) develop TBWRCP predictive equations for children using TBWdil as the criterion method, (b) cross-validate the derived equations, (c) determine precision of the TBWRCP method, and (d) compare the criterion method TBWdil with three methods of estimating TBW: RCP, MFBIS and anthropometry.Predictive equations, independent of sex, were developed with linear regression in a group of 36 children. The relationship between combined RCP frequency shifts and TBWdilution had an r2 = 0.90 and standard error of the estimate (SEE) =1.42 kg. Multiple regression analysis, that included a term for body mass index, only had a small effect on r2 = 0.93 and SEE = 1.25 kg. In vivo TBW precision for the vertical, horizontal and combined frequency modes ranged from 0.7 to 3.4%. Bland–Altman analysis indicated close agreement between the criterion method TBWdil and the three other methods of TBW estimation. Mean differences were TBWRCP(2) = 0.01 ± /− 1.34 kg, TBWMFBIS = 0.45 ± /− 1.35 kg, TBWAnthropometry = 0.29 ± /− 1.29 kg.Currently the RCP method does not significantly improve the prediction of TBW compared to MFBIS and anthropometry in this initial study. However the derived equation was independent of sex and body size had only a small effect.

Validity of anthropometry- and impedance-based equations for the prediction of total body water as measured by deuterium dilution in Cameroonian haemodialysis patients

There is no available information on the validity of anthropometry- and impedance-based equations for predicting total body water (TBW) in Cameroonian haemodialysis patients. This study aimed to validate and develop predictive equations of TBW for Cameroonian haemodialysis patients. TBW in 40 Cameroonian haemodialysis patients (28 men and 12 women) was measured by deuterium dilution and compared with the one predicted by 7 anthropometric and 9 BIA equations. Multiple linear regression analysis was used to develop an equation for predicting TBW as measured by deuterium, from anthropometric parameters. Pure errors in predicting TBW showed unacceptable value for all equations tested. In all the cases, unacceptable discrepancies at individual level for clinical purposes were noted. The following equation was developed and showed a better agreement with the deuterium dilution method: TBW=13.8994+0.0017×Age+0.3190×Weight+1.8532×Sex. Further development and cross-validation of anthropometric and BIA prediction equations specific to African heamodialysis patient are needed. Meanwhile, the equation developed in this study which provided a better agreement with the isotope dilution could be use for Cameroonian haemodialysis patients.

Estimation of total body water and extracellular water with bioimpedance in athletes: A need for athlete-specific prediction models

Bioelectrical impedance analysis (BIA) equations can predict total body water (TBW) and extracellular water (ECW) in non-athletic healthy populations. This study aimed: a) to develop BIA-based models for TBW and ECW prediction based on dilution methods in a sample of national level athletes; and b) to validate the new models with a cross-validation approach in a separate cohort using dilution methods as criterion. Two hundred and eight highly trained athletes (21.3±5.0 years) were evaluated during their respective competitive seasons. Athletes were randomly split into development (n=139) and validation groups (n=69). The criterion method for TBW was deuterium dilution and for ECW was bromide dilution, where ICW was the respective difference between both. Resistance (R) and reactance (Xc) were obtained with a phase-sensitive 50kHz BIA device and used for the estimation of TBW and ECW. Athletic BIA-based models were developed for TBW and ECW [TBW=0.286+0.195*S(2)/R+0.385*Wt+5.086*Sex; ECW=1.579+0.055*S(2)/R+0.127*Wt+0.006*S(2)/Xc+0.932*Sex, where sex is 0 if female or 1 if male, Wt is weight (kg), S is stature (cm), and R and Xc are in ohm (Ω)]. Cross validation revealed R(2) of 0.91 for TBW and R(2) 0.70 for ECW and no mean bias. The new equations can be considered valid, with no observed bias, thus affording practical means to quantify TBW and ECW in national level athletes.

Mean Expected Error in Prediction of Total Body Water: A True Accuracy Comparison between Bioimpedance Spectroscopy and Single Frequency Regression Equations.

For several decades electrical bioimpedance (EBI) has been used to assess body fluid distribution and body composition. Despite the development of several different approaches for assessing total body water (TBW), it remains uncertain whether bioimpedance spectroscopic (BIS) approaches are more accurate than single frequency regression equations. The main objective of this study was to answer this question by calculating the expected accuracy of a single measurement for different EBI methods. The results of this study showed that all methods produced similarly high correlation and concordance coefficients, indicating good accuracy as a method. Even the limits of agreement produced from the Bland-Altman analysis indicated that the performance of single frequency, Sun's prediction equations, at population level was close to the performance of both BIS methods; however, when comparing the Mean Absolute Percentage Error value between the single frequency prediction equations and the BIS methods, a significant difference was obtained, indicating slightly better accuracy for the BIS methods. Despite the higher accuracy of BIS methods over 50 kHz prediction equations at both population and individual level, the magnitude of the improvement was small. Such slight improvement in accuracy of BIS methods is suggested insufficient to warrant their clinical use where the most accurate predictions of TBW are required, for example, when assessing over-fluidic status on dialysis. To reach expected errors below 4-5%, novel and individualized approaches must be developed to improve the accuracy of bioimpedance-based methods for the advent of innovative personalized health monitoring applications.

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.

Prediction of body water compartments in preterm infants by bioelectrical impedance spectroscopy

To evaluate nutritional interventions in preterm infants, a simple, accurate assessment of the type of growth, that is, change in body composition through the relative contributions of lean body tissue and fat mass to weight gain, is needed. Bioelectrical impedance may provide such a method. The aim of this study was to develop resistivity coefficients appropriate for use in bioelectrical impedance spectroscopy (BIS) analysis of body water volumes in preterm infants. A total of 99 preterm infants were enrolled (mean gestational age 32 completed weeks). Total body water (TBW) and extracellular water (ECW) were determined using the reference methods of deuterium and bromide dilution. BIS measurements taken at the same time allowed calculation of resistivity coefficients. Predictions of TBW and ECW obtained using these coefficients were then validated against volumes determined using the reference methods in a separate cohort of infants. Data were available for 91 preterm infants. BIS-predicted TBW and ECW correlated well with the measured volumes (Pearson's r(p)=0.825 and 0.75, respectively). There was a small bias (TBW 10 ml and ECW 40 ml) but large limits of agreement (TBW ± 650 ml and ECW ± 360 ml). BIS appears to have limited clinical utility; however, the relatively small bias means that it may be useful for measurements within a population or for comparisons between groups in which population means rather than individual values are compared.

A critical analysis of whole body bioimpedance spectroscopy (BIS) for the estimation of body compartments in health and disease

Aim of the study was to assess the accuracy and precision of a BIS device and the relative contribution of BIS beyond the anthropometric parameters. The output of the Impedimed device (SFB7) and the relative contribution of height, weight, age, sex and resistance values at zero and infinite frequency (Rzero and Rinf respectively) to the prediction of total body water (TBWd, deuterium space), of extracellular fluid (ECFbr, sodium bromide space) and of fat mass (FMDXA) were assessed in 116 subjects (32 healthy subjects and 84 patients with disorders of body composition). Using a repeated randomization procedure, new equations for TBW, ECF and FM were derived.The SFB7 gave measures of determination similar to those obtained with equations that included only anthropometric data. The SFB7, but not the newly derived regression equations, underestimated TBW and ECF by 3.82±3.37 (mean±SD) and by 0.93±2.62l and overestimated FM by 6.55±3.86kg. Nine of 16 patients with ECF overload as detected by ECFbr were also detected by BIS. BIS measurements contribute marginally but not significantly beyond anthropometric data to the prediction of TBW, ECF and FM, either in healthy subjects or in patients with disturbed body composition.

Development of height-weight based equation for assessment of body composition in Sri Lankan children

To develop a height and weight based equation to estimate total body water (TBW) in Sri Lankan children. Cross sectional descriptive study done involving 5-15 year old healthy children. Height and weight were measured. TBW was assessed using isotope dilution method (D(2)O) and fat free mass (FFM) calculated. Multiple regression analysis was used to develop prediction equation and validated using PRESS statistical technique. Height, weight and sex code (male=1; female=0) were used as prediction variables. This study provides height and weight equation for the prediction of TBW in Sri Lankan children. To the best of our knowledge there are no published height weight prediction equations validated on South Asian populations. Results of this study need to be affirmed by more studies on other closely related populations by using multicomponent body composition.

Estimation of total body water from bioelectrical impedance spectroscopy in oncology outpatients receiving radiotherapy and agreement with three prediction equations

Bioelectrical impedance spectroscopy (BIS) may be more accurate in determining total body water (TBW) than bioelectrical impedance analysis (BIA). The present study compared the agreement between three TBW prediction equations developed using BIA and BIS-derived TBW in oncology outpatients. A cross-sectional, observational study was conducted in 37 outpatients receiving radiotherapy (27 males/10 females, aged 68.3 +/- 10.2 years). TBW was estimated by BIS (TBW(BIS)) and three BIA TBW prediction equations (TBW(ca-u): underweight cancer patients; TBW(ca-n): normal-weight cancer patients; and TBW(rad): patients receiving radiotherapy). Bland-Altman analyses determined agreement between methods. BIS-derived TBW using new resistivity constants was calculated. The mean +/- SD of TBW estimated by BIS was 39.8 +/- 8.3 L, which was significantly different from the prediction equations; TBW(rad) 35.1 +/- 7.9 L, TBW(ca-u) 33.1 +/- 7.5 L and TBW(ca-n) 32.3 +/- 7.3 L, (P < 0.001). Using new resistivity constants, TBW was 36.2 +/- 8.1 L but this still differed from the equations (P < 0.001). Bias between TBW(BIS) and that predicted by the equations was in the range 4.7-7.4 L or 1.1-3.9 L using new resistivity constants. TBW estimated by BIS cannot be directly compared with oncology-specific BIA equations, suggesting that BIS cannot be used at the group level in outpatients receiving radiotherapy. There was a reduced bias with BIS using new resistivity constants; however, further research should determine any advantage of BIS over BIA in this population.

Validity of impedance-based predictions of total body water as measured by 2H dilution in African HIV/AIDS outpatients.

Measurements of body composition are crucial in identifying HIV-infected patients at risk of malnutrition. No information is available on the validity of indirect body composition methods in African HIV-infected outpatients. Our first aim was to test the validity of fifteen published equations, developed in whites, African-Americans and/or Africans who were or not HIV-infected, for predicting total body water (TBW) from bioelectrical impedance analysis (BIA) in HIV-infected patients. The second aim was to develop specific predictive equations. Thirty-four HIV-infected patients without antiretroviral treatment and oedema at the beginning of the study (age 39 (SD 7) years, BMI 18.7 (SD3.7) kg/m2, TBW 30.4 (SD7.2) kg) were measured at inclusion then 3 and 6 months later. In the resulting eighty-eight measurements, we compared TBW values predicted from BIA to those measured by 2H dilution. Range of bias values was 0.1-4.3 kg, and errors showed acceptable values (2.2-3.4 kg) for fourteen equations and a high value (10.4) for one equation. Two equations developed in non-HIV-infected subjects showed non-significant bias and could be used in African HIV-infected patients. In the other cases, poor agreement indicated a lack of validity. Specific equations developed from our sample showed a higher precision of TBW prediction when using resistance at 1000 kHz (1.7 kg) than at 50 kHz (2.3 kg), this latter precision being similar to that of the valid published equations (2.3 and 2.8 kg). The valid published or developed predictive equations should be cross-validated in large independent samples of African HIV-infected patients.

Validity of impedance-based equations for the prediction of total body water as measured by deuterium dilution in Cameroonian HIV-infected patients treated with antiretroviral treatment

No information is available on the validity of impedance-based equations for the prediction of body composition in Cameroonian HIV-infected patients treated with antiretroviral drugs. Equations for the prediction of total body water (TBW) have the tendency to be population-specific, and this may be due to biological factors, such as variable body geometry and physiological state. We tested the validity of equations derived from different racial backgrounds for predicting TBW from bioelectrical impedance analysis measurements. The TBW content of 56 Cameroonian HIV patients (19 men and 37 women) treated with the first-line ARV regimen was measured by deuterium dilution and compared with those predicted by 12 equations developed respectively in samples of white, black, black and white, or unspecified racial background subjects. Pure errors in predicting TBW showed acceptable value for all the equations tested. Four equations (three from whites and one from blacks and whites) yielded a non-significant bias; however, equation H which presented the narrower 95% confidence interval and the smaller pure error was recommended for the prediction of TBW in Cameroonian HIV-infected patients treated with antiretroviral drugs. In all other cases, we observed either an overestimation or underestimation of TBW with variable bias values. The absence of a clear trend in cross-validation among equations according to their origin and the probable effect of physiological state should encourage further exploration of the causes of the lack of validity.

A Prediction Equation for Total Body Water in Spanish Children.

Total body water (TBW) is the largest molecular body compartment and comprises 73.2% of fat free mass (FFM). Accurate TBW measurements are fundamental for body composition estimations, although assessing TBW with accuracy is difficult and expensive, which make non-reference methods important to apply in epidemiological and clinical settings. Accurate and reliable predictive equations to determine TBW in children are lack, and we are unaware of specific equations developed for young Spanish population. Moreover, development of accurate tools to assess body composition in children is a cornerstone in the context of pediatric obesity. PURPOSE: The aim of this study was to develop a child-specific TBW prediction equation in Spanish children, aged 12 to 18 yrs, using the isotope dilution technique as the reference method. METHODS: Sixty-two healthy boys participated in this study (age 14.8 ± 1.9, stature 168.6 ± 9.0 cm, weight 65.5 ± 16.2 kg, and BMI 22.8 ± 4.4 kg.m−2). The selected independent variables were: girths and skinfolds measures (performed using the traditional protocols) and TBW obtained using a non-reference method [(bioelectrical impedance analysis (Medisystem, Sanocare Human System SL, Spain)]; whole body resistance (R) and reactance (Z) were assessed, then the impedance index was derived (ht2/R). TBW from the reference method was the dependent variable, and was obtained by deuterium dilution (D2O-TBW) using a stable Hydra gas isotope ratio mass spectrometer (PDZ, Europe Scientific, UK). Stepwise regression analysis was applied to identify the variables that most accurately estimated TBW. Twenty three boys were used to cross-validate the previous derived equation. Statistical significance was set at p<0.05. RESULTS: A new TBW prediction equation was developed for young Spanish children. The best equation incorporated ht2/R and weight (R2 = 0.91; SEE= 2.0 kg). The pure error was 1.03 kg. TBW (kg) = 0.495 ht2/R + weight x 0.107 + 6.08. CONCLUSIONS: In the present report, we derived and validated anthropometric predictive equation, which demonstrated to be accurate and reliable in healthy young male Spanish population. These equations may be used for accurate epidemiological studies in this specific population.

Assessment of body composition in Sri Lankan children: validation of a bioelectrical impedance prediction equation

To develop bioelectrical impedance analysis (BIA) equations to predict total body water (TBW) and fat-free mass (FFM) of Sri Lankan children. Data were collected from 5- to 15-year-old healthy children. They were randomly assigned to validation (M/F: 105/83) and cross-validation (M/F: 53/41) groups. Height, weight and BIA were measured. TBW was assessed using isotope dilution method (D(2)O). Multiple regression analysis was used to develop preliminary equations and cross-validated on an independent group. Final prediction equation was constructed combining the two groups and validated by PRESS (prediction of sum of squares) statistics. Impedance index (height(2)/impedance; cm(2)/Omega), weight and sex code (male=1; female=0) were used as variables. Independent variables of the final prediction equation for TBW were able to predict 86.3% of variance with root means-squared error (RMSE) of 2.1 l. PRESS statistics was 2.1 l with press residuals of 1.2 l. Independent variables were able to predict 86.9% of variance of FFM with RMSE of 2.7 kg. PRESS statistics was 2.8 kg with press residuals of 1.4 kg. Bland Altman technique showed that the majority of the residuals were within mean bias+/-1.96 s.d. Results of this study provide BIA equation for the prediction of TBW and FFM in Sri Lankan children. To the best of our knowledge there are no published BIA prediction equations validated on South Asian populations. Results of this study need to be affirmed by more studies on other closely related populations by using multi-component body composition assessment.