Woodrow G, Oldroyd B, Turney J H, Davies P S, Day J M, Smith M A
Renal Unit, Leeds General Infirmary, UK.
Clin Nephrol. 1997 Jan;47(1):52-7.
Studies of the effect of Kt/V (urea) on prediction of outcome in patients on peritoneal dialysis have shown conflicting results. We performed this study to examine the effects of the measurement of V by varying techniques on the calculation of Kt/V, using body water estimated by deuterium oxide dilution (D2O dilution) as the criterion method for estimation of V. Studies were performed in 20 peritoneal dialysis patients. Kt was calculated from 24-hour dialysate and urine collections and V estimated by D2O dilution, Watson formulae, 58% of body weight, bioelectrical impedance (BIA) and 73% of fat-free mass estimated by DEXA. V was also measured in 35 healthy controls. Hydration, expressed as body water by D2O dilution as a percentage of fat-free mass estimated by DEXA did not differ between peritoneal dialysis patients 71.0 (4.9)% and a healthy control group 71.1 (5.0)%. Mean Kt/V using D2O dilution was 2.14 (0.36). The other techniques resulted in a significantly lower Kt/V; Watson equations 2.01 (0.35), p < 0.005, BIA 1.93 (0.31), p < 0.0001, DEXA 2.06 (0.28), p < 0.05, 58% body weight 1.83 (0.38), p < 0.0001. Limits of agreement of Kt/V by the simpler techniques compared with D2O dilution [mean difference of (other techniques -D2O dilution) as % of mean values +/- 95% limits of agreement] were Watson equation -5.9 +/- 15.3%, BIA -10.1 +/- 15.5%, DEXA -3.4 +/- 13.5% and 58% body weight -9.9 +/- 23.5%. Differences in Kt/V from estimates using D2O dilution were significantly negatively correlated with body fat for 58% body weight (r = -0.80, p < 0.0001) and the Watson formulae (r = -0.49, p < 0.05) but not for BIA or DEXA. We conclude that clinically significant variation in Kt/V may occur due to the estimation of V and may account for the uncertainty of the value of Kt/V as a predictor of outcome in peritoneal dialysis patients. Estimating V by BIA and DEXA did not have any benefit over the Watson formulae in terms of agreement with D2O dilution, though did avoid systematic errors related to body fat. Estimation of V as a fixed proportion of body weight is clearly inferior to the other techniques.
关于Kt/V（尿素）对腹膜透析患者预后预测作用的研究结果相互矛盾。我们开展本研究，以氘稀释法（D2O稀释法）估算的机体水分作为V估算的标准方法，探讨不同技术测量V对Kt/V计算结果的影响。研究纳入20例腹膜透析患者。通过收集24小时透析液和尿液计算Kt，并采用D2O稀释法、Watson公式、体重的58%、生物电阻抗分析法（BIA）以及双能X线吸收法（DEXA）估算的无脂肪体重的73%来估算V。同时测量了35名健康对照者的V。以D2O稀释法测得的机体水分占DEXA估算的无脂肪体重的百分比表示的水合状态，在腹膜透析患者（71.0 [4.9]%）与健康对照组（71.1 [5.0]%）之间无差异。采用D2O稀释法时，平均Kt/V为2.14（0.36）。其他技术得出的Kt/V显著更低；Watson公式为2.01（0.35），p<0.005；BIA为1.93（0.31），p<0.0001；DEXA为2.06（0.28），p<0.05；体重的58%为1.83（0.38），p<0.0001。与D2O稀释法相比，较简单技术计算的Kt/V的一致性界限[（其他技术 - D2O稀释法）的平均差值占平均值的百分比±95%一致性界限]为：Watson公式-5.9±15.3%，BIA-10.1±15.5%，DEXA-3.4±13.5%，体重的58%-9.9±23.5%。对于体重的58%（r=-0.80，p<0.0001）和Watson公式（r=-0.49，p<0.05），与采用D2O稀释法估算的Kt/V差异与体脂呈显著负相关，但BIA或DEXA与体脂无此相关性。我们得出结论，由于V估算方法的不同，Kt/V可能出现具有临床意义的差异，这可能是导致Kt/V作为腹膜透析患者预后预测指标时不确定性的原因。就与D2O稀释法的一致性而言，采用BIA和DEXA估算V并不优于Watson公式，不过可避免与体脂相关的系统误差。将V估算为体重的固定比例明显不如其他技术。
