DIALYSIS ADEQUACY INDICES AND BODY COMPOSITION IN MALE AND FEMALE PATIENTS ON PERITONEAL DIALYSIS

The assessment of solute removal by the kidneys in normal subjects and patients with chronic kidney disease is usually based on a reference such as solute distribution volume (typically total, or extracellular body water), mass/concentration of the particular solute in the body (or in a particular body compartment), or body surface area. Whereas most authors agree that renal function (glomerular filtration rate) should be expressed in relation to size-related features, the choice of the relevant reference for solutes removed by dialysis is debated (1-5). The assessment of dialysis adequacy, which before the 1980s was based on blood solute concentration, is nowadays mostly based on the fractional fluid volume cleared of the solute during the treatment, KT/V. In peritoneal dialysis (PD), two scaling methods have been used: for urea KT/V, urea removal is normalized to total body water (TBW, V = TBW), whereas creatinine clearance, Cl(1.73/BSA), is adjusted to body surface area (BSA). The problem of the choice of scaling of dialysis adequacy indices was widely discussed for hemodialysis (HD), and, in particular, the choice between KT/V, KT/BSA and KT; however, there was no generally accepted consensus (1,2,6-9). Following the observation that both dialysis dose as measured by clearance multiplied by dialysis time (KT) and total body water (V) are independent predictors of patient survival, the question arises as to whether KT/V, i.e., the ratio of those two parameters, is a meaningful index for defining dialysis adequacy. Furthermore, while KT/V initially was thought to be an operational parameter, which could be used to prescribe and monitor dialysis dose independently of patient body size, this may not be the case, at least not in PD. As reported by Tzamaloukas et al. (4), both urea KT/V and creatinine clearance correlate with body mass and BSA in PD. They demonstrated an inverse relationship between KT/V and body mass (and equivalent indices), whereas KT was found to be independent of patient body size. As previously noted by Tzamaloukas et al. as well as by studies in HD patients (1-4,10), dialysis dose should take body composition into account. Dialysis adequacy indices: urea KT/V and creatinine clearance, Cl(1.73/BSA), approved for assessing PD efficiency, include in their formulas normalization by TBW and BSA, respectively. Body size-and-composition-related features may have an impact on both: normalized and non-normalized (solute plasma concentration, dialysate over plasma concentration ratio, CD/CP, KT) measurements performed in patients on dialysis. This is likely to be of particular importance when prescribing dialysis dose in obese and underweight patients, but also in women and men. Anthropometric indices and body composition are in general different in males and females, as is survival on dialysis (2,4,11,12). As suggested by Lowrie et al. smaller patients may require proportionately greater total dose than larger patients to achieve comparable survival (11). The aim of the current study was therefore to analyze the impact of anthropometric and body composition-related features (BSA, TBW, body mass index (BMI), weight, height, fat mass (FM), and fat-free mass (FFM)) on dialysis adequacy indices and their components (KT/V, KT, plasma concentration, dialysate over plasma concentration ratio, removed mass and clearances for urea and creatinine) in PD patients with special attention to gender differences.