Accuracy of an on-line urea monitor compared with urea kinetic model and direct dialysis quantification

To verify the accuracy of a urea monitor (UM) to assess dialysis adequacy, it was compared with a modified direct dialysis quantification method (mDDQ) and with a Casino modified urea kinetic model (mUKM) algorithm. Simplified Jindal and Daugirdas formulas, an anthropometric body water Watson formula, bioelectric impedance analysis, and the Garred model have also been considered. Concerning urea removal, UM results are close to mDDQ, as are the predialytic blood urea nitrogen values obtained by UM in the initial equilibration test. Urea distribution volume results for UM, mDDQ, and bioelectric impedance analysis are similar, whereas it appears clearly overestimated by the Watson formula. Urea monitor clearances are not significantly different from mDDQ, unlike UM Kt/V, which is slightly higher than mDDQ reference value, although with a satisfactory degree of concordance. Rebound effect must be considered by sampling after the equilibration time (et) when mUKM or simplified Kt/V formulas are used: mUKMet Kt/V results are quite similar to mDDQ, as is the Daugirdas value. Regarding NPCR, UM results are neither significantly different from mDDQ nor from the Garred model, whereas mUKM results are significantly overestimated. When rebound is considered, NPCR by mUKMet and NCPR by mDDQ are identical. The UM approach is simple and practical, with a satisfactory degree of reliability for clinical practice.