Development of a population-specific regression equation to estimate total body water in hemodialysis patients (original) (raw)

1997, Kidney International

Development of a population specific regression equation to estimate total body water in hemodialysis patients. We have previously shown that the impedance index (height corrected resistance) is a valid and reliable correlate of total body water (TBW) in hemodialysis patients. We estimated TBW by single frequency bioelectrical impedance analysis (BIA) in 3009 in-center hemodialysis patients, and developed an ESRDspecific TBW equation from routinely available demographic and anthropometric variables. The mean SD age was 60.5 15.5 years; 47% were female, 47% African-American, and 36% diabetic. Dialysis duration was 3.8 3.7 years. Mean TBW was 40.8 9.3 kg, 56 9% of body weight. A stepwise linear regression equation was fit on a two-thirds random sample, deriving significant parameter estimates for the variables age, gender, height, weight, diabetic status, weight squared, and the crossproducts of age and gender, age and weight, gender and weight, and height and weight. The equation was then validated in the remaining one-third sample, and compared with TBW estimates by the Watson and Hume-Weycr formulae. TBW estimated by our equation (40.6 8.6 kg) was not significantly different from the BIA TBW (40.5 9.3 kg). In contrast, TBW estimated by the Watson (37.0 7.6 kg) and Hume-Weyer (37.9 7.7 kg) formulae underestimated TBW by a mean of 3.5 and 2.6 kg, respectively. A population-specific equation provides superior prediction of TBW in hemodialysis patients. The use of formulae developed and validated in non-uremic populations may result in underestimates of TBW in patients with ESRD, and potentially, overestimates of dialysis dose approximated by the clearance-time to TBW ratio (Kt/V). TBW resides in the skeletal muscle, TBW may serve as a proxy for somatic protein stores [1]. In end-stage renal disease (ESRD), TBW is of additional importance, as it approximates the volume of distribution of urea. An estimate of TBW is frequently used to calculate the clearance time-product (Kt) to volume (V) ratio, a marker of dialysis adequacy. This ratio can be misinterpreted if V is over-or underestimated [21. Several means of estimating the urea volume of distribution are commonly used. The formal method uses