Total EKR expresses the total clearance (dialytic + renal), i.e. the sum of the contribution of the dialyser urea clearance (Kd) to EKR (EKRd) and of the residual renal urea clearance (Kru). According to the FTM, the total target EKR should remain constant: 12 ml/min/35 L. This means that each ml/min of Kru should be replaced by increasing EKRd by the same amount. In contrast, according to the VTM, the total target EKR is 12 ml/min/35 L − Kru, i.e. it varies from a minimum value at the start of HD treatment (in this case Kru = 6 ml/min/35 L) to a maximum value when Kru = 0 (modified from Figure 1 of reference 15).