The equivalent renal urea clearance: a new parameter to assess dialysis dose

Currently the total (dialytic plus renal) urea clearance (KT) is computed as Kt/V plus the equivalent Kt/V (KT/VKR) provided by the renal urea clearance (KR). However, KT/VKR is computed with two different formulae, by Gotch and Keshaviah respectively. Moreover Teschan suggested a weekly KT, that is a multiple of Keshaviah's KT. We suggest the equivalent renal urea clearance (EKR), that kinetically quantifies the "time-averaged KT' and is independent of treatment type and schedule.

Computer simulation has been used to analyse the relationship between EKR, as corrected for urea volume (EKRc), and Kt/V. Data from 66 HD patients, of whom eight were on once-weekly and 11 on twice-weekly HD, had been used to compare EKR with current KTs.

For each individual schedule, the relationship between EKRc and Kt/V is linear and each ml/min of KR increases EKR by the same amount. For instance, for thrice-weekly HD patients, EKRc = 1 + 10 x Kt/V: so that, the critical Kt/V values of 0.8 and 1.0 correspond to EKRc values of 9.0 and 11 ml/min respectively, independently from treatment type and schedule. As to the clinical data, all once- and twice-weekly patients had a significant KR and excellent clinical status, but most of them had 9 < or = EKRc < 11 ml/min. After appropriate reconciliation of units, it has been found that kinetic KT was overestimated by about 10-12% (range, 2-23%) by Keshaviah and Teschan's KT, and by about 2-7% (range, 0.3-15%) by Gotch's KT.

EKRc can account for KR and provide guidelines for all types of dialysis treatments: as far as urea is concerned, dialysis adequacy should require EKRc > or = 11 ml/min. However, it is likely that EKRc > or = 9 ml/min could suffice for patients with a substantial residual renal function.