How to Test for Peritoneal Dialysis Adequacy
Peritoneal dialysis adequacy is assessed through two primary measurements: (1) quantifying solute removal via weekly Kt/Vurea and creatinine clearance from 24-hour dialysate and urine collections, and (2) characterizing peritoneal membrane transport properties using standardized tests like the Peritoneal Equilibration Test (PET). 1
Core Adequacy Measurements
Solute Clearance Assessment
Measure both weekly Kt/Vurea and total creatinine clearance (normalized to 1.73 m² BSA) every 4 months to quantify the actual amount of solute removed from the body. 1
Target a weekly Kt/Vurea of at least 1.7 as the minimum adequacy threshold. 2
Collect 24-hour dialysate and urine samples when the patient is clinically stable to calculate these parameters accurately. 1
Wait at least 1 month after any peritonitis episode before performing adequacy testing, as peritonitis transiently increases peritoneal transport characteristics and yields falsely elevated clearance measurements. 3
Timing of Initial Measurements
Perform the first adequacy measurement 2 weeks after initiating PD in patients without substantial residual kidney function (RKF), as waiting longer risks inadequate dialysis. 1
For patients with significant RKF, measure adequacy at 4 weeks after starting dialysis to allow stabilization of peritoneal membrane characteristics. 1
Measure RKF every 2 months in patients on "incremental" PD prescriptions to ensure timely dose adjustments as kidney function deteriorates. 1
Once weekly Kt/V from RKF falls below 0.1, routine RKF measurement can be discontinued as it becomes negligible. 1
Peritoneal Membrane Transport Testing
Test Selection and Baseline Establishment
Each center should select one standardized test (such as PET, Standard Peritoneal Permeability Analysis, or Peritoneal Dialysis Capacity test) and use it consistently for all patients. 1
The Peritoneal Equilibration Test (PET) is the simplest and most widely used test with the most clinical experience, making it the practical choice for most centers. 1
Establish baseline peritoneal membrane transport characteristics 4-8 weeks after initiating daily PD therapy, as the first month shows transient increases in D/P ratios that don't reflect stable membrane function. 1, 4
Use a modified PET with 3.86%/4.25% dextrose when specifically evaluating patients with ultrafiltration failure. 1
When to Repeat Transport Testing
- Repeat peritoneal membrane transport testing when clinically indicated, including:
- Changes in ultrafiltration capacity
- Difficulty achieving adequacy targets
- Significant changes in clinical status
- At least 1 month after peritonitis resolution 1
Additional Monitoring Components
Nutritional Assessment
Monitor serum albumin levels and estimate dietary protein intake (DPI) using normalized protein nitrogen appearance (nPNA) when obtaining 24-hour collections. 1
Evaluate nutritional status monthly as part of routine PD patient assessment. 1
Practical Implementation Considerations
Recognize that adequacy measurements depend heavily on patient cooperation in collecting dialysate, recording volumes accurately, and performing the full prescription on collection day. 1
The measurement reflects only that particular day's dialysis, not necessarily average clearance, which is a key limitation of current testing methods. 1
For automated PD (APD) patients, cyclers with monitoring mechanisms can help verify compliance, though this increases treatment cost. 1
Common Pitfalls to Avoid
Never test during active peritonitis or within 1 month of resolution, as this yields unreliable results with falsely elevated clearances. 3
Don't rely solely on urine output as a marker of declining RKF in patients on incremental PD—directly measure RKF every 2 months. 1
Avoid using actual body weight when calculating V in obese patients; consider using ideal or standard weight instead, though evidence is limited. 1
Don't assume drain volume alone predicts membrane transport characteristics—formal PET testing provides more accurate classification. 1