Pre-HD Renal Function Testing in Hemodialysis Patients
Direct Recommendation
Measure residual kidney function (RKF) when residual urea clearance is ≥2 mL/min, and reassess every 3-4 months using 24-hour urine collections to guide dialysis prescription adjustments and preserve remaining kidney function. 1
Why Residual Kidney Function Matters
RKF is more strongly associated with patient outcomes than dialysis dose itself, making its assessment and preservation a critical priority in HD management. 1
Patients with significant RKF (>2 mL/min urea clearance) represent 10-30% of the HD population and require different management strategies than those without residual function. 1
RKF provides continuous clearance between dialysis sessions, reduces hemodynamic instability, and may protect against cardiovascular complications through mechanisms beyond simple toxin removal. 1, 2
When to Measure RKF
Measure RKF at baseline for all new HD patients to establish whether they fall above or below the 2 mL/min threshold. 1
Reassess every 3-4 months in patients with RKF >2 mL/min using 24-hour urine collections for urea clearance calculation. 1, 2
Measure within 3 months prior to any dialysis prescription modeling that will incorporate residual kidney clearance into the dose calculation. 1
How to Incorporate RKF into Dialysis Prescription
Include residual kidney urea clearance (Kru) in the standardized Kt/V calculation when measured clearance is ≥2 mL/min, which increases the calculated stdKt/V by approximately 7% on average. 1
Below the 2 mL/min threshold, RKF can be ignored in dose calculations to avoid the complexity and expense of serial measurements in patients where it provides minimal benefit. 1
For patients with substantial RKF, twice-weekly dialysis may be permissible if function is stable and interdialytic weight gains are not excessive, but this requires close monitoring. 1
Transition to thrice-weekly dialysis must occur promptly as RKF declines below adequate levels to prevent underdialysis. 1
Strategies to Preserve RKF
Avoid intradialytic hypotension, which damages residual kidney function through ischemic injury. 2
Use lower dialysate temperatures, slower blood flow initiation, and gentle fluid removal to minimize hemodynamic instability. 2
Prescribe ultrafiltration rates that balance euvolemia with hemodynamic stability rather than aggressive fluid removal that compromises blood pressure. 1, 3
Avoid overly aggressive ultrafiltration even when targeting dry weight adjustments, as this can irreversibly damage remaining nephrons. 4
Use loop diuretics cautiously in patients with RKF to promote sodium and water loss, but avoid overzealous dosing that worsens renal function. 4
Critical Pitfalls to Avoid
Do not ignore RKF >2 mL/min when calculating dialysis adequacy, as this leads to unnecessary dialysis time and compromises quality of life. 1
Do not add Kru to dose calculations without recent measurement (within 3 months), as this risks underdialysis if function has declined. 1
Do not assume RKF is stable—serial measurements are essential because function typically declines over time and prescription adjustments must follow. 1
Do not prescribe twice-weekly dialysis without documented substantial RKF, as this is inadequate for most patients and increases mortality risk. 3