The Peritoneal Equilibration Test (PET) is a diagnostic assessment for individuals undergoing peritoneal dialysis (PD). It provides information about the peritoneal membrane, a thin tissue lining the abdomen and covering abdominal organs. The PET helps understand how effectively this membrane functions as a filter in dialysis. By evaluating its transport properties, the test guides personalized dialysis treatment plans.
Purpose of the Peritoneal Equilibration Test
Each patient’s peritoneal membrane acts as a unique filter, with varying efficiency in removing waste products and excess fluid. The PET measures these individual differences. It assesses how quickly waste substances, such as urea and creatinine, move from the blood into the dialysate fluid in the abdominal cavity.
It also evaluates how rapidly glucose from the dialysate is absorbed by the body. This absorption rate directly impacts how much water can be removed during a dialysis exchange. Understanding these transport characteristics allows healthcare providers to tailor the dialysis prescription for each patient.
The PET Procedure
The PET begins with the patient draining any existing dialysate fluid. Then, about 2 liters of a standardized 2.5% dextrose dialysis solution is infused into the peritoneal cavity via the catheter. This infusion takes about 10 minutes, and patients may roll to ensure proper mixing.
The fluid then remains in the abdomen for a four-hour “dwell time.” During this period, patients can move or rest. Small dialysate samples are collected at set intervals: immediately after infusion (0-hour), and then at two and four hours into the dwell. A blood sample is also drawn at the two-hour mark to compare solute concentrations. The procedure concludes with complete fluid drainage, a final sample, and total drain volume measurement.
Interpreting PET Results
PET results categorize the peritoneal membrane into one of four transport types, based on how quickly substances move across it. Classifications are determined by analyzing the dialysate-to-plasma (D/P) ratio of substances like creatinine, and the dialysate-to-initial dialysate (D/D0) ratio of glucose over the dwell time. This reveals the membrane’s permeability and capacity for fluid removal.
A High Transporter membrane moves waste products, such as creatinine, quickly from the blood into the dialysate, often showing a D/P creatinine ratio greater than 0.80 after four hours. However, rapid transport also means glucose from the dialysate is absorbed quickly, which can reduce ultrafiltration during longer dwell times. In contrast, a Low Transporter membrane moves waste products more slowly, resulting in lower D/P creatinine ratios, between 0.34 and 0.49. This slower glucose absorption allows for excellent ultrafiltration, as the osmotic gradient is maintained longer.
The two intermediate categories are High-Average Transporter and Low-Average Transporter, representing membranes with balanced transport characteristics. High-Average transporters show a D/P creatinine ratio between 0.66 and 0.81, while Low-Average transporters fall in the range of 0.50 to 0.64. These classifications guide treatment adjustments.
How Results Influence Dialysis Treatment
Insights from the PET directly tailor each patient’s peritoneal dialysis prescription, ensuring optimal waste removal and fluid balance. For High Transporters, shorter dwell times are prescribed to prevent excessive glucose absorption and maintain effective ultrafiltration. These individuals are well-suited for automated peritoneal dialysis (APD), also known as “the cycler,” which performs multiple short exchanges overnight.
Conversely, Low Transporters benefit from longer dwell times, as their membrane’s slower solute transport allows for sustained fluid removal and waste clearance. This makes them ideal candidates for continuous ambulatory peritoneal dialysis (CAPD), where manual exchanges are performed fewer times daily with extended dwell periods. Glucose concentration in the dialysis solution may also be adjusted based on PET results; for example, high transporters might use lower glucose concentrations or alternative osmotic agents like icodextrin to improve ultrafiltration and avoid reabsorption. This personalized approach maximizes the effectiveness of peritoneal dialysis therapy.