Dialysis adequacy from pre/post BUN.
URR = ((Pre-BUN − Post-BUN) / Pre-BUN) × 100. KDOQI minimum: URR ≥ 65% (target ≥ 70%). URR is simpler than Kt/V but doesn't account for ultrafiltration. Inadequate URR is associated with increased mortality. If URR < 65%, increase treatment time, blood flow, or dialyzer size.