MEASUREMENT OF KT V IN PERITONEAL-DIALYSI S - EFFECT OF DIFFERENT ESTIMATIONS OF UREA DISTRIBUTION VOLUME/

The result of calculating Kt/V peritoneal dialysis varies with the met hod used to calculate the volume of distribution of urea. The formulae of Watson (W) Hume (H) and the percentile method (%), in which volume of distribution is calculated from anthropometric measurement are mos t widely used; the relation between results by these methods is theref ore of great importance. We studied the relationship between Kt/V calc ulated by these methods (Kt/V-W, Kt/V-H, Kt/V-%) employing the method of Bland and Altman which expresses results, not as correlation coeffi cients but as the distribution of differences between the means, expre ssed graphically, and the limits of agreement [d-1.96SD, d + 1.96SD] w hen d = difference between means and SD = standard deviation. Compared with Kt/V-W as reference, the correction for Kt/V-H was between 1.10 and 0,92 and for Kt/V-% between 0,82 and 1.21. This indicates that Kt/ V-H differs from Kt/V-W by +8% to -10% and Kt/V-% by -18% to +21%. Thi s questions the interchangeability of these measurements and suggests that the percentile method is not suitable for assessing the volume of distribution of urea in CAPD patients.