Measurement Of Total Body Water Research Articles

Measurements of total body water with a foot-to-foot impedancemeter

The objective was to set-up a method for measuring total body water volumes (TBW) using a Tefal foot-to-foot impedancemeter (FFI) by comparison with a multifrequency medical impedancemeter and to validate this method against deuterium dilution data. The investigation was carried out in 57 Caucasian adult subjects. Impedancemeters were a Tefal Bodymaster Vision ® (foot-to-foot) featuring a square wave signal and a Xitron Hydra 4200 ® (5–1000 kHz) using BIS method. TBW was measured by the Xitron using a new method that we have developed which applies the BIS method directly to extra and intracellular fluids combined. Although the high frequency impedance of the FFI ( R hf) was higher than the Xitron infinite frequency resistance and corresponded to a frequency around 100 kHz, TBW differences between the FFI and Xitron were not significant, 0.17 ± 2.17 L for men ( P = 0.694) and 0.04 ± 1.88 L for women ( P = 0.902). Then, our method was tested on another Caucasian population in which R hf had been measured with the same FFI, together with TBW measurements by deuterium dilution. TBW differences between the FFI and dilution were −0.38 ± 2.27 L for men ( P = 0.237) and −0.72 ± 2.37 L for women ( P = 0.06). Our method permits, at least in a Caucasian healthy population, to measure TBW using this FFI with the same accuracy as a whole body multifrequency medical impedancemeter, and the measurement, made in upright position, is much quicker.

Hyperhydrating with glycerol: effects on thermoregulation, hydration and athletic performance during specific exergonic exercise in a warm-humid environment

We investigated the effects of hyperhydration with glycerol vs. water on athletic performance under hot-humid conditions (30% relative humidity and 36° C). During a 10-day acclimation period, 14 competitive male oarsmen performed 90 minutes of exercise at 260-W. On the eleventh day, athletes hydrated by consuming in 90 minutes a nutrient drink with or without glycerol. After hydration, athletes were tested three times with 250–400-W workloads in 30-W steps, at 15-min intervals. During the 250–400-W tests, athletes rehydrated with water (control and glycerol A groups) or with flavored glycerol solution (glycerol B group). Measurements of total extracellular body water (EBW) by bioelectric impedance analysis indicated a statistically significant increase in water retention (approximately 525 ml) and decreased lactate at aerobic threshold for the glycerol B group compared to the control and glycerol A groups following the exercise tests. The performance on the three 250–400-W tests was stable for glycerol B athletes but decreased for glycerol A and control groups. The 15-W difference observed at the aerobic threshold between glycerol B and control groups was estimated to translate into a 37-m competitive advantage during a 6-min Olympic rowing competition.

Body-composition assessment in infancy: air-displacement plethysmography compared with a reference 4-compartment model

Background: A better understanding of the associations of early infant nutrition and growth with adult health requires accurate assessment of body composition in infancy.Objective: This study evaluated the performance of an infant-sized air-displacement plethysmograph (PEA POD Infant Body Composition System) for the measurement of body composition in infants.Design: Healthy infants (n = 49; age: 1.7–23.0 wk; weight: 2.7–7.1 kg) were examined with the PEA POD system. Reference values for percentage body fat (%BF) were obtained from a 4-compartment (4-C) body-composition model, which was based on measurements of total body water, bone mineral content, and total body potassium.Results: Mean (±SD) reproducibility of %BF values obtained with the PEA POD system was 0.4 ± 1.3%. Mean %BF obtained with the PEA POD system (16.9 ± 6.5%) did not differ significantly from that obtained with the 4-C model (16.3 ± 7.2%), and the regression between %BF for the 4-C model and that for the PEA POD system (R2= 0.73, SEE = 3.7%BF) did not deviate significantly from the line of identity (y = x).Conclusions: The PEA POD system provided a reliable, accurate, and immediate assessment of %BF in infants. Because of its ease of use, good precision, minimum safety concerns, and bedside accessibility, the PEA POD system is highly suitable for monitoring changes in body composition during infant growth in both the research and clinical settings.

Total body water measurement by a modification of the bioimpedance spectroscopy method

We propose a method for calculating directly total body water (TBW) volumes (V (t)) from whole body resistance extrapolated at infinite frequency (R (infinity)) using a XITRON 4200 impedance meter. Mean TBW resistivities for men and women were determined from measurements of R (infinity) and fat-free mass (FFM(d)) measured by DXA in 58 healthy subjects assuming an average hydration coefficient of 73.2%. Mean differences between V (t) measured by our new method and those deduced from DXA data were +0.11 +/- 1.61 L for women and +0.13 +/- 2.16 L for men. For validation, this method was tested with the same resistivities against a 2nd group of 16 volunteers and the mean difference between V (t) from impedance and DXA was -0.80 +/- 1.43 L. Since the resistance at 50 kHz (R (50)) was found to be equal, in average, to 1.230 R (infinity) for men and 1.223 R (infinity) for women, this method can also be applied at 50 kHz with a similar accuracy by estimating R (infinity) from R (50). When our new method was applied to the monitoring of water loss during 28 dialysis runs performed on 13 patients, it predicted a mean water loss equal to 94% of ultrafiltered volume.

Measurements of total body water with a foot-to-foot impedance meter

Measurements of total body water with a foot-to-foot impedance meter

Development of a foot-to-foot impedancemeter for measuring body composition during exercise

Foot-to-foot impedancemeters (FFI) are cheaper, simpler and quicker to use than medical type impedancemeters. The purpose of this work was to increase the functions of a prototype FFI derived from a commercially available FFI (Tefal Bodymaster Vision ,Rumilly, France) with performing electronics, in order to obtain extracellular (ECW), total body water (TBW) volumes, body cell mass (BCM) and muscle mass in addition to weight and fat-free mass. A modification of the FFI permitted also to use it with hand and feet reusable electrodes. ECW and TBW measurements with the FFI were achieved by comparison with measurements made using a multifrequency medical impedancemeter Hydra 4200 (Xitron Tech, San Diego) and Dual X ray absorptiometry and appropriate modifications of the bioimpedance spectroscopic (BIS) method (1, 2). For BCM and muscle mass, we used Kotler’s and Wang’s methods respectively to relate them to the total body potassium concentration TBK as BCM = 0.0083 TBK, Muscle mass=0.0093 TBK+0.024 Age-3.21 where TBK is expressed in terms of Xcp, the equivalent reactance at 50 kHz, the subject height H, and his weight W. These methods were applied on a group of 52 children: 12 controls did not practice exercise, 20 jogged intermittently and 20 jogged regularly for three months. Changes in all the physiologic parameters listed above during this period as well as improvement in running speed for the three groups were compared and will be reported. With further development, this FFI prototype, which is easy to

Bioelectrical impedance analysis in the measurement of the body composition of surgical patients.

The evaluation of nutritional status in surgical patients remains a difficult problem. Bioelectrical impedance analysis (BIA) is a new method of body composition analysis which is easily performed at the bedside. This study determined the accuracy of BIA in the measurement of total body water (TBW) and potassium (TBK) in a heterogeneous group of surgical patients. The resistance and reactance components of impedance were measured with a whole body impedance analyser. Tritiated water dilution and whole body monitoring were the reference methods for TBW and TBK analysis. With the BIA technique the coefficient of variation for the estimation of TBW was 8.1 per cent and for TBK was 6.4 per cent. Allowing for the errors of the reference methods these results show that BIA is of limited value in the estimation of TBW but may provide a useful index of TBK.

Multi-element analysis of the living body by neutron activation analysis-application to critically ill patients receiving intravenous nutrition.

Neutron activation analysis has been used to determine the total content in the body of N, K, Na, Cl, P and Ca in 25 critically ill surgical patients before and after a 14-day course of intravenous nutrition. Muscle elemental composition was also determined in these patients at the same time as the total body analysis. Over the 14-day period of intravenous feeding the total body contents of all the measured elements increased (2-9.7 per cent) but only the increase in K was statistically significant. Muscle chemistry suggested an intracellular K depletion which was corrected over the study period. The results of the total body multi-element analysis were interpreted to show a mean gain of 1.25 l of extracellular fluid and 0.51 l of intracellular fluid and direct measurement of total body water suggested that this interpretation was probably valid. The first application of the technique to patients with nutritional and metabolic problems has quantified the weight gained by two body compartments during a 2-week period of intravenous nutrition. Its further application should help to solve a number of nutritional and metabolic problems in clinical surgery.

The serum sodium concentration after surgical operation: precision permits predictions.

In view of previous conflicting reports, the distribution of a water overload was investigated in 6 healthy volunteers. The fall in serum sodium was predictable from prior measurement of total body water (tritium) confirming that the induced hyponatraemia was dilutional. Using a standard intravenous fluid regimen, a prospective study for 6 days on 50 patients undergoing major abdominal surgery established a confidence band for change in serum sodium concentration. This band not only enables precise prediction of whether observed sodium values in patients are "normal' for that point in their postoperative course, but also demonstrates that changes are more prolonged than was at first thought. Their dilutional nature following uncomplicated surgery is supported by linear relationships between serum osmolality and serum sodium (s-Osm = 1.86 [s-Na+] + 18:74; (P < 0.001) and between observed and calculated osmolality (Obs-Osm = 0.97 [Calc-Osm] + 15.11; P < 0.001). More detailed investigation of 14 patients by isotope dilution provided independent evidence of dilutional change. This conclusion is additionally supported by lesser changes in patients on a more restricted fluid regimen. As a practical confirmation of the utility of this approach, departures from the simple dilutional relationships were observed in 7 critically ill patients whose postoperative course was complicated. In this group osmolal "gags' of 20-50 mosmol/kg were identified. Current standard postoperative fluid regimens cause dilutional changes; these are predictable and provide a yardstick for use in management of both the healthy and the ill surgical patient.

Reliability in Estimates of Body Composition of Birds: Oxygen‐18 versus Deuterium Dilution

Body composition in birds was evaluated indirectly by 18O and 2H dilution. Body composition was determined by whole-body chemical analysis of eight adult roosters (Gallus gallus). In vivo measurements of total body water (TBW) were carried out using doubly labeled water (2H2 18O). Estimated dilution spaces using both the plateau and intercept approaches were compared with the results obtained by carcass lyophilization. Both 18O and 2H slightly overestimated TBW compared with the results obtained by lyophilization, by 2.2%+/-1.9% and 5.7%+/-0.2%, respectively; both differences were statistically significant (P<0.01). The difference between these isotope estimations was significant (P<0.001). However, isotope dilution spaces and TBW were highly correlated. There was a strong inverse relationship between total body fat and TBW percentages (r2=0.98, P<0.0001). The relation between TBW and body protein was significant. Water content in lean body mass (72.8%) obtained in our study was very close to that reported in mammals, demonstrating no fundamental difference in tissue water content between birds and mammals. Estimated body fat and protein values from isotopic dilution did not significantly differ from values obtained by direct chemical analysis (P>0.05), except for body fat in the Pace and Rathbun approach (Table 3). Although estimation of TBW and body composition by isotope dilution is time consuming and expensive, deuterium offers a reliable and low-cost alternative compared with 18O. The advantage of in vivo estimation of TBW with isotopic dilution in combination with the regression approach is that it permits repeated measurements of body composition on the same birds under laboratory and free-living conditions.

Skinfold Prediction Equation for Athletes Developed Using a Four-Component Model

Skinfold (SKF) equations exist to predict percent body fat (%BF) in athletes; however, none have been derived from multicomponent model reference measures. To develop and cross-validate a %BF prediction equation based on SKF in athletes using a four-component model as the reference measure. Subjects were 132 collegiate athletes (20.7 +/- 2.0 yr; 78 males: 28 black, 50 white; 54 females: 10 black, 44 white). Four-component model estimates of %BF (%BF4C) included measures of total body water from deuterium dilution, bone mineral by dual- energy x-ray absorptiometry (DXA), and body density by densitometry using underwater weighing. SKF measures included subscapular, triceps, chest, midaxillary, suprailiac, abdominal, and thigh sites (7SKF). A prediction equation was developed on 102 athletes using 7SKF, race, and gender as predictor variables. Cross-validation was performed on a representative holdout sample of 30 athletes. The equation cross-validated well (slope and intercept both not different (P > 0.05) from the line of identity (LOI); r(YY') = 0.85, total error (TE) = 3.76%BF) and was better than the existing athlete SKF equations (intercept and slope both different from LOI (P < 0.01); r(YY') = 0.76, TE = 4.51%BF). Notably, a prediction equation developed using 3SKF sites (abdomen, thigh, and triceps) produced a similar accuracy (intercept and slope both not different from LOI (P > 0.05); r(YY') = 0.85, TE = 3.66%BF). The new 7SKF equation improved on SKF equations developed using densitometry. The final equation based on the whole sample was %BF' = 10.566 + 0.12077*(7SKF) - 8.057*(gender) - 2.545*(race). Moreover, a 3SKF equation was comparable in accuracy to the 7SKF equation: BF' = 8.997 + 0.24658*(3SKF) - 6.343*(gender) - 1.998*(race).

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

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. 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. 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. 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. 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.

Estimation of total body water from foot‐to‐foot bioelectrical impedance analysis in patients with cancer cachexia – agreement between three prediction methods and deuterium oxide dilution

Bioelectrical impedance analysis (BIA) is a useful bedside measure to estimate total body water (TBW). The aim of this study was to determine the agreement between three equations for the prediction of TBW using BIA against the criterion method, deuterium oxide dilution, in patients with cancer cachexia. Eighteen measurements of TBW using foot-to-foot BIA in seven outpatients with cancer cachexia (five male and two female, age 56.4 +/- 6.7 years) at an Australian hospital. Three prediction formulae were used to estimate TBW - TBW(ca-radiotherapy) developed in patients with cancer undergoing radiotherapy, TBW(ca-underweight) and TBW(ca-normal weight) developed in underweight and normal weight patients with cachexia. TBW was measured using the deuterium oxide dilution technique as the gold standard. Mean measured TBW was 39.5 +/- 6.0 L. There was no significant difference in measured TBW and estimates from prediction equations TBW(ca-underweight) and TBW(ca-radiotherapy). There was a significant difference in measured TBW and TBW(ca-normal weight). All prediction equations overestimated TBW in comparison with measured TBW. The smallest bias was observed with TBW(ca-underweight) (0.38 L). The limits of agreement are wide (>7.4 L) for each of the prediction equations compared with measured TBW. At a group level, TBW(ca-underweight) is the best predictor of measured TBW in patients with cancer cachexia. For an individual however, the limits of agreement are wide for all prediction equations and are unsuitable for use. Practitioners need to be aware of the limitations of using TBW prediction equations for individuals.

Validation of estimates of total body water in pediatric dialysis patients by deuterium dilution

Current K-DOQI recommendations call for an assessment of dialysis adequacy that depends critically on an estimate of total body water (TBW). Such estimates are problematic in children since the range of patient size is large, and often formulas derived in normals are not validated in end-stage renal disease. Gold standard methods of TBW measurement, such as deuterium dilution ((2)H(2)O), are not appropriate in the clinical setting, yet noninvasive methods such as bioimpedance analysis (BIA) and dual energy x-ray absorptiometry (DEXA) have not been independently validated. We studied 14 stable pediatric dialysis patients on 1 to 3 occasions using (2)H(2)O dilution, BIA, DEXA, and anthropometry to measure TBW. We compared our data set to previously published formulae for TBW to determine root mean square error (RMSE) and skew of the estimate. TBW prediction based upon the anthropometric formula proposed by the Pediatric Peritoneal Dialysis Consortium provided the best fit to our independent data set with RMSE = 2.15 L, and no skew by Bland-Altman analysis. Other formulas produced large, clinically relevant errors; obese subjects confounded many estimates. TBW calculated from hydrated lean body mass from DEXA scan was reliable with RMSE = 1.03 L and no skew. BIA-derived estimates can be useful, although the magnitude of RMSE ranged from 1.45 to 6.24 L, and one formula produced skewed results. Techniques for estimating TBW in pediatric dialysis patients must be validated by independent data sets before being incorporated into clinical and research practice.

The use of near infrared interactance in hemodialysis

Forty‐one consecutive admissions to a hemodialysis center were evaluated. Demographic information including age, gender, race, and diagnosis was collected. Patients, &gt;18 years old, with end stage renal disease and on hemodialysis for at least one year were included. Those with edema or known ascites were excluded. Weight was measured before and after hemodialysis (HD) using a standard scale and by considering the amount of fluid loss by the hemodialysis machine. Body composition including total body water (TBW) was calculated before and after HD using near infrared interactance (NIR). All measurements were completed during half hour before and after HD. Forty‐one patients included: men (n = 26), women (n = 15); median age 58 (range 28–88 years). Twenty‐eight were African American and the rest Caucasians. The amount of intravascular fluid taken after HD (assessed by weight reduction) ranged 0–5 L with median 2.2 L. NIR analysis for the same patients at the same time showed different total body water measurements in 91% of cases (P &gt; 0.05). Moreover, NIR analysis showed increase in total body water in 24% of patients even though the hemodialysis machine showed a loss of total body water; median of 1.3 (range: 0–3L). The error in measuring body composition with NIR was both large and varied (random and not systematic error). We conclude that NIR analysis cannot be considered as a reliable method to evaluate body composition, especially total body water, amongst patients with end stage renal disease undergoing hemodialysis.

Deuterium dilution: the time course of 2H enrichment in saliva, urine, and serum.

Total body water (TBW) volume can by measured in humans by administering an oral dose of an isotope tracer, such as 2H2O or H218O, and measuring the isotope enrichment in saliva, urine, or serum samples. Although serum has long been considered the medium of choice for measuring isotope enrichment because of rapid tracer equilibration (1), urine or saliva sampling is less burdensome to the patient. However, the measurement of isotope enrichment was found to be less reliable in urine than in serum, possibly because of a longer time period for isotopic equilibration of the bladder contents relative to serum (2). Schoeller et al. (1) suggested that saliva was an acceptable medium for measurement of TBW using 2H218O because isotopic equilibration occurred within 3 h and provided results similar to those obtained in serum. In another study, the enrichments of 2H in saliva and plasma were identical and reached a plateau 2 h after administration of an oral 10-g dose of 2H2O (3). To our knowledge, there have been no within-subject comparisons of the time to achieve a 2H enrichment plateau in saliva, urine, and serum samples obtained simultaneously. The purpose of this study, therefore, was to determine the time course for isotope equilibration of 2H in saliva, urine, and serum and the level of agreement in 2H enrichment among these media. This information can be applied to protocols for measurement of TBW in clinical and research settings (4)(5). Five healthy, weight-stable, nonobese women [mean (SD) body mass index, 22.1 (2.0) kg/m2], 20 to 43 years of age, provided written informed consent and completed the study. The study was approved by the Colorado Multiple Institutional Review Board. The …

Validation of fan beam dual energy x ray absorptiometry for body composition assessment in adults aged 18–45 years

Background: Pencil beam dual energy x ray absorptiometry (DXA) has been shown to provide valid estimates of body fat (%BF), but DXA fan beam technology has not been adequately tested...

Effect of Sex on Reproducibility of Bioimpedance Derived Total Body, Extracellular, and Intracellular Fluid Volumes

1669 Total body, extracellular, and intracellular fluid volumes are useful measures for some types of exercise physiology research. Previous research has indicated acceptable reproducibility of multifrequency bioelectrical impedance analysis (BIA) derived body fluid volumes in mixed populations. However, sex specific data has not been reported. Purpose: To examine the effect of sex on reproducibility of multifrequency BIA derived total body water (TBW), extracellular fluid (ECF), and intracellular fluid (ICF) volumes. Methods: Fourteen subjects (age = 26 ± 8 yrs, height = 172 ± 12 cm, weight = 77 ± 18 kg, 8 female) were assessed on five separate occasions over a two week period. Precautions included avoidance of data collection during one week prior to menses, an overnight fast, 12 hr abstention from alcohol, caffeine, and exercise, standardized measurement time (± 1 hr), electrode placement, and limb abduction. Following a 10- minute supine equilibration period single measurements of TBW, ECF, and ICF were performed.TableResults: For each variable for both sexes, intraclass correlation coefficients (ICC) were high, and showed no significant differences between any days. Coefficients of variation (CV) were low for each variable and for both sexes, indicating adequate sensitivity to detect small changes in fluid volumes (ranging from ± 0.3 L for female ICF to ± 1.4 L for male TBW). Conclusion: Sex has no effect on reproducibility of BIA derived TBW, ECF, and ICF when standardized precautions are taken. Multifrequency BIA would be useful to monitor the responses of body fluid volumes to training, nutritional, medicinal, or heat stress interventions in males and females.

Total body water measurements using resonant cavity perturbation techniques

A recent paper proposed a novel technique for determining the total body water (TBW) of patients suffering with abnormal hydration levels, using a resonant cavity perturbation method. Current techniques to measure TBW are limited by resolution and technical constraints. However, this new method involves measuring the dielectric properties of the body, by placing a subject in a large cavity resonator and measuring the subsequent change in its resonant frequency, fres and its Q-factor. Utilizing the relationship that water content correlates to these dielectric properties, it has been shown that the measured response of these parameters enables determination of TBW. Results are presented for a preliminary study using data estimated from anthropometric measurements, where volunteers were asked to lie and stand in an electromagnetic screened room, before and after drinking between 1 and 2 l of water, and in some cases, after voiding the bladder. Notable changes in the parameters were observed; fres showed a negative shift and Q was reduced. Preliminary calibration curves using estimated values of water content have been developed from these results, showing that for each subject the measured resonant frequency is a linear function of TBW. Because the gradients of these calibration curves correlate to the mass-to-height-ratio of the volunteers, it has proved that a system in which TBW can be unequivocally obtained is possible. Measured values of TBW have been determined using this new pilot-technique, and the values obtained correlate well with theoretical values of body water (r = 0.87) and resolution is very good (750 ml). The results obtained are measurable, repeatable and statistically significant. This leads to confidence in the integrity of the proposed technique.

Urea space and total body water measurements by stable isotopes in patients with acute renal failure

Knowledge of urea volume of distribution (Vurea) in patients with acute renal failure (ARF) is critical in order to prescribe and monitor appropriate dialytic treatment. We have recently shown that in ARF patients, Vurea estimation by urea kinetic modeling is significantly higher than total body water (TBW) by anthropometric estimation. However, these estimates of Vurea and TBW have not been validated by isotopic methods, considered as reference measurement standards. In this study, we measured Vurea by [13C]urea and TBW by deuterium oxide (D2O) in 21 patients with ARF (14 males, 7 females, age 62.0 +/- 10.6 years old, 83% Caucasian, 17% African American) at three different centers. These measurements were compared to TBW estimates from anthropometric and bioelectrical impedance (BIA) measurements. Our results show that Vurea by [13C]urea (51.0 +/- 11.7 L) is significantly higher than TBW estimated by all other methods (TBW by D2O: 38.3 +/- 9.8 L, P < 0.001; TBW by BIA: 45.7 +/- 15.7 L, P= 0.08; TBW by Watson formula: 38.3 +/- 7.3 L, P < 0.001; TBW by Chertow formula: 39.3 +/- 7.8 L, P= 0.002, all versus Vurea). Despite significant overestimation of the absolute value and considerable variation, Vurea significantly correlated with TBW by BIA (r= 0.66, P < 0.01) and TBW by D2O (r= 0.5, P= 0.04). There was also significant correlation between D2O and BIA determined TBW (r= 0.8, P < 0.001). In terms of useful guidelines to prescribe a specific dose of dialysis in patients with ARF, conventional estimates of TBW as surrogates for Vurea should be used with caution. We propose that these conventional estimates of TBW should be increased by approximately 20% (a factor of 1.2) to avoid significant underdialysis.