The Peritoneal Equilibration Test and similar tests measure how well the peritoneal membrane functions, and should be done 4 to 8 weeks after starting PD, and repeated if dialysis or fluid removal problems occur. This test is useful in guiding the physician in writing and changing the patient’s PD prescription. The PET test should always be performed when the patient is clinically stable. It should never be performed within one month of an episode of peritonitis. Other tests that measure peritoneal function are the SPA (standard peritoneal permeability analysis) and PDC (peritoneal dialysis capacity). The preference of one test over another varies from dialysis center to center. Membrane function influences the amount of time (dwell time) dialysate stays in the belly. The amount of clearance during an exchange depends on the transport rate or speed the peritoneal membrane allows urea, creatinine and other molecules to move from the patient’s blood across the peritoneal membrane into the dialysate. Everyone’s transport rate is not the same. The PET establishes each individual’s peritoneal membrane transport rate. The PET will show if a patient’s peritoneal membrane is a high (fast), average or low (slow) transporter.

It is assumed high transporters require shorter dwell times; and low transporters require longer dwell times (up to 6 hours per exchange). Generally, peritoneal membrane function remains the same over time but may change due to peritonitis or technique failure. It is believed high transport is the consequence of systemic inflammation or chronic damage to the lining of the blood vessels. The result of being a high transporter is inadequate fluid removal, but this can often be improved with nocturnal intermittent PD, which offers shorter, more frequent exchanges. 

When a PET shows a change has occurred, the dialysis prescription may need to be changed. Low transporters generally need longer dwell times while high transporters require shorter dwell times and an increased number of exchanges. If a patient notices easy fatigue or shortness of breath, that he/she is unable to control his/her fluid weight, his/her blood pressure is higher, or there seems to be a decrease in drain volume, it is very important to bring this to the attention of the medical team, particularly if he/she has recently had peritonitis. Any change in PD stability requires a new PET test be performed. It should not be done for at least one month after an illness, hospitalization or peritonitis episode.