We thank you for your question. The standardized Peritoneal Equilibration Test (PET) requires you to send the first sample of PD fluid from a drain of at least 20 minutes after an overnight dwell. Now, bear in mind, in 1987, when the PET was first described by Twardowski, all patients were on CAPD, therefore the standard overnight dwell time was around 8─12 hours (1). In a follow up study, Twardowski found that results for a PET were satisfactory with any preceding dwell time longer than 3 hours (when looking at small solute clearances, e.g. creatinine and urea) (2). Other researchers have reported similar findings (3,4).
 
In a recent report in Peritoneal Dialysis International entitled “Peritoneal Equilibration Testing: Your questions answered”, the authors commented “The test begins with an overnight 8–12 hour pre-exchange” and that “while some work suggests that shorter preceding dwell times may be sufficient, the long dwell remains standard practice” (5). An informal survey of members of our IPSD Nursing Committee (Australia, Brazil, Canada, UK, USA) found that in most PD units the nurses are familiar with generally do a 2 L 2.5% dwell overnight ― 8─12 hours, then 2 L 2.5% exchange for the standard PET. However, if a patient is too small to tolerate a 2 L fill, then they adjust the overnight volume down to 1.5 L and do the PET using a 1.5 L fill volume to match. Also, one nurse reported that in her country the modified PET using a 4.25% PD solution is used, but also the 2.5% for the standard PET. For patients on automated peritoneal dialysis (APD), most nurses reported that they switch the patient to CAPD overnight with a long (8─12 hour) dwell (2 L fill, 2.5%,) before the PET.  However, one nurse said for the PET that they routinely have their patients on APD start the APD early the night before, then come to the PD unit having had the last fill dwell for at least 6─8 hours, another nurse reported similarly, that the last fill is used for the dwell before beginning the actual PET.
 
In summary, to answer your specific question, for the PET, the 8─12 hour dwell overnight with a 2 L fill, 2.5% PD solution is relatively standard still, especially for patients on CAPD; however, for patients on APD, while many PD centers have their patients switch to a long CAPD dwell overnight (8─12 hours), others have their patients remain on APD, but use the dwell of the last fill before beginning the actual PET.
 
1.Twardowski ZJ, Nolph KD, Khanna R, et al. Peritoneal equilibration test. Perit Dial Bull 1987; 7:138–47.
 
2.Twardowski ZJ, Prowant BF, Moore HL, et al. Short peritoneal equilibration test: impact of preceding dwell time. Adv Perit Dial 2003; 19:53–8.
 
3.Figueiredo AE, Conti A, Poli de Figueiredo CE. Influence of the preceding exchange on peritoneal equilibration test results. Adv Perit Dial 2002; 18:78-80.
 
4.Lilaj T, Vychytil A, Schneider B, Hörl WH, Haag-Weber M. Influence of the preceding exchange on peritoneal equilibration test results: a prospective study. American journal of kidney diseases. 1999 Aug 1;34(2):247-53.
 
5.Gu J, Bai E, Ge C, Winograd J, Shah AD. Peritoneal equilibration testing: Your questions answered. Peritoneal Dialysis International. Published online November 9 2022;0(0). doi:10.1177/08968608221133629