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Interpreting the Peritoneal Equilibration Test (PET)
By Rainer Himmele, MD, MSHM Vice President, Medical Information & Education, Fresenius Medical Care North America & Corinne E. Zeller-Knuth, Ph.D., Principal Medical Information Scientist, Fresenius Medical Care North America & Amy Janik, BSN, RN, Principal Medical Information Clinician, Fresenius Medical Care North America
Using data from the original 103 patients, Twardowski created these standardized equilibration curves that are still in use today. The solid white line is the average equilibration ratio for that population. One standard deviation up or down—the dashed white lines—then sets the cutoffs between high and high-average transporters and low and low-average transporters. The outer edges of the blue and green areas represent the maximum and minimums for the group. Generally, patients are categorized based on the 4-hour D/P creatinine and D/D0 glucose ratios. For example, if the 4-hour D/P creatinine is 0.59 and the 4-hour D/D0 glucose is 0.47, the patient would be classified as low average. Some labs may not report the D/P urea ratios or urea transport classification, but the urea data may be required for prescription modeling. Importantly, the transport type classification should be consistent among the three measures.3
USING THE PET TO OPTIMIZE PD PRESCRIPTIONS
There are published recommendations of clinical implications for PD prescriptions based on PET transport type. High and high-average transporters equilibrate rapidly. This means their transports for urea and creatinine are fast, but it also means they lose the glucose gradient rapidly, so ultrafiltration is limited. These patients would do best with more frequent exchanges with shorter dwells in order to avoid reabsorption. PD Plus or Icodextrin should be considered for daytime dwells. It may be possible to have dry periods if the patient has good residual renal function.
On the other hand, low and low-average transporters equilibrate slowly. This means their transports for urea and creatinine are slower, which results in good ultrafiltration with minimal reabsorption, even for a long day dwell. But they may require longer dwells with higher-volume exchanges in order to get adequate clearance.
While the PD prescription has to be individualized for every patient, general recommendations for PD regimens based on PET transport type have been given. For high transporters, short exchanges with a cycler may be well suited and it may be possible to have dry periods if there is good residual renal function. High-average transporters may do cycler or manual exchanges, and dry days may be possible in some cases. For low-average, good residual renal clearance CAPD or CCPD is possible, meaning continuous 24-hour therapy with no dry periods. Without significant residual function, high-dose CAPD, meaning larger-dwell volumes, may be necessary. For low transporters of average body size, high-dose CAPD may work best. For larger low-transport patients, achieving PD adequacy, goals may be more challenging and require some creativity with their individual PD prescription.
POTENTIAL ERRORS OF THE PET AND HOW TO MINIMIZE THEM
Here are some common mistakes than can influence PET results. Prior to the PET, not doing the overnight long dwell or incompletely draining the overnight dwell or, for diabetic patients, not testing blood glucose to ensure levels are less than 235 mg/dL can lead to inaccurate results. During the actual PET, not following the standardized procedure with a 2-L fill, 2.5% glucose, not filling and draining within the specified times, not taking samples at the right times, incomplete mixing of the samples or lack of ambulation for patient during the dwell can all affect the PET results. Lastly, errors in labeling or samples getting switched can happen. As mentioned before, it is also important to check the validity of the PET lab results (i.e., the transport type classification should be consistent among the three measures of glucose, creatinine, and urea).
- van Biesen W, Heimburger O, Krediet R, Rippe B, La Milia V, Covic A, Vanholder R, ERBP working group on peritoneal dialysis. Evaluation of peritoneal membrane characteristics: clinical advice for prescription management by the ERBP working group. Nephrol Dial Transplant. 2010;25(7):2052-2062. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20203287
- Misra M, Khanna R. The clinical interpretation of peritoneal equilibration test. Semin Dial. 2014;27(6):598-602. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25139767
- Twardowski ZJ, Nolph KO, Khanna R, Prowant BF, Ryan LP, Moore HL, Nielsen MP. Peritoneal Equilibration Test. Perit Dial Int. 1987;7(3):138-148. Available from: http://www.pdiconnect.com/cgi/content/abstract/7/3/138
- Blake P, Burkart JM, Churchill DN, Daugirdas J, Depner T, Hamburger RJ, Hull AR, Korbet SM, Moran J, Nolph KD. Recommended clinical practices for maximizing peritoneal dialysis clearances. Perit Dial Int. 1996;16(5):448-456. Available from: http://www.ncbi.nlm.nih.gov/pubmed/8914175
- Misra M, Khanna R. Peritoneal Equilibration Test. UpToDate. 2018;Topic 1972 (Version 14.0).
- Misra M, Khanna R. The clinical interpretation of peritoneal equilibration test. Semin Dial. 2014;27(6):598-602. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25139767.
- Prowant BF, Moore HL, Twardowski ZJ, Khanna R. Understanding discrepancies in peritoneal equilibration test results. Perit Dial Int. 2010;30(3):366-370. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20424200.
Appendix: Sample PET lab report