In Costa Rica, continuous ambulatory peritoneal dialysis (CAPD) was introduced in the late eighties, initially with few patients as a short-term renal replacement therapy. Currently, social security covers around one hundred fifty adult patients (2/3 of which are men) distributed in four main hospitals around the country.
Patients undergoing CAPD exhibit a wide variability in the peritoneal transport of solutes and fluids. Measuring the characteristics of peritoneal membrane transport is important for the characterization of the functional state as for the prescription of the adequate dose of dialysis therapy in an individual fashion [
In our country an adequate characterization of the type of peritoneal transport has not been done yet. Our population presents marked ethnic differences as compared with those for which the test was described. In previous studies significant differences have been found in reference values for D/D0 glucose and D/P creatinine for different populations using the same standardized PET [
For these reasons, we aim to establish the reference values for the Costa Rican population and to determine the influence of different clinical factors on the type of peritoneal transport.
The standardized Twardowski et al. [
Following the night exchange and 8–12 hours of dwell time, the totality of the abdominal cavity was drained and new exchange was introduced with 2 liters of glucose 4.25% peridial solution this was performed in the supine position and mobilizing the patient every 2 minutes to insure an adequate mixture of the dialysate solution in the abdominal cavity. Shortly after, dialysis solution samples and blood samples were taken at 0, 2, and 4 hours. After 4 hours, the dialysate solution was drained and its volume was quantified. Glucose, creatinine, C reactive protein, and albumin were measured in each sample, using conventional techniques with a colorimetric assay. There was no need to use are a correction factor for creatinine in the peritoneal fluid, because it was proven that its quantification with the equipment used is zero, in spite of the high glucose concentrations in a new peridial solution bag [
Using our own values for D/P creatinine, a patient was classified as a high transporter if his D/P is 1 standard deviation (SD) above the mean (
A sample size of thirty patients was calculated with the objective of determining the proportion of average transporters (high and low), with an 18% of precision. We took as reference an expected proportion of average transporters of 68%, as suggested by previous studies [
The data is presented as mean
A
The characteristics of the population studied are represented in Table
Characteristics of the population studied in the three compared groups.
Variable |
Twardowski cohort [ |
Mexican cohort [ |
Costa Rican cohort |
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Age (years) | NR |
|
|
Male gender (%) | NR | 41 (47.7) | 25 (83.33) |
Diabetes mellitus (%) | 18 (20.9) | 35 (40.7) | 19 (63.33) |
Therapy time (weeks) |
|
|
|
Peritonitis during treatment (%) | 0 | 2 (2.3) | 9 (30) |
Albumin (g/dL) | NR |
|
|
C reactive protein (mg/dL) | NR |
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|
NR: not reported.
Peritoneal transportation according to the clinical characteristics of the population under study.
Variable | Type of transporter |
| |||
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Low |
Low-average |
High-average |
High |
||
Age (years) |
|
|
|
|
0.34 |
Male gender (%) | 5 (20) | 9 (36) | 8 (32) | 3 (12) | 0.47 |
Diabetes mellitus (%) | 4 (21.1) | 8 (42.1) | 6 (31.6) | 1 (5.3) | 0.47 |
Peritonitis (%) | 1 (11.1) | 4 (44.4) | 3 (33.3) | 1 (11.1) | 0.92 |
Dialysed volume (L) |
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0.19 |
Therapy time (weeks) |
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|
0.20 |
Albumin (g/dL) |
|
|
|
|
0.84 |
C reactive protein (mg/dL) |
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|
0.62 |
The comparisons of the PET values obtained by D/P creatinine and by D/D0 glucose at 2 and 4 hours in our population and those obtained in the original population by Twardowski et al. [
Comparison between the ratio of solutes and dialysis volume drained in the original, the Mexican, and the Costa Rican population.
Twardowski et al. [ |
Mexican cohort [ |
Costa Rican cohort | |
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Drained volume (L) |
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In Latin America very few studies have been made to validate the PET in this region. PET is a feasible technique used to tailor the CAPD prescription and a very important tool to predict poor outcomes. Since much variability has been observed in the PET results, it is recommended to perform this test early in treatment in each CAPD Unit [
If our sample were categorized according to the reference values provided by Twadorski et al. [
Besides, in comparison with the Mexican cohort, our sample exhibited a lower creatinine D/P ratio at 0 hours. This can be the result of heterogeneous residual dialysate volumes. However, neither the Mexican study nor our research determined this volume and proper conclusion could not be drawn. Similarly, glucose D/D0 ratios at 2 and 4 hours were lower in our cohort than in the Mexican and original population. This result may be due to high dialysate glucose absorption as well as a consequence of eventual errors in nursing procedures or laboratory measurements.
We must highlight that the composition of each compared population was different. Sixty-three percent of our sample was diabetic and one third of our patients had a history of peritonitis. Both of these variables were significantly different in our sample and can also explain our findings. Several studies, with conflicting results, have revealed histopathological alterations in the peritoneal membrane of diabetic patients leading to increased glucose absorption [
It is remarkable that the ultrafiltrate volume is one of the variables that differ in a greater magnitude, both in the original population and in the Mexican cohort, since the volume variable was larger in our sample. This is not in concordance with our findings of D/D0 for glucose, which is significantly smaller at 4 hours and indicates larger glucose absorption from the dialysis solution. It suggests that other nonosmotic stimuli can explain how the ultrafiltrate volume independently varies from the glucose concentration of the dialysate. In animal models, it has been suggested that 50% of the transperitoneal water flow occurs through ultrasmall pores, known as aquaporins 1 whose expression is not completely related with osmotic stimuli [
It is important to note that in comparison with the original and Mexican population we used a 4.25% dextrose solution instead of the 2.5% dextrose exchange. Although previous findings have determined that D/D0 glucose and D/P creatinine are similar with the use of either 4.25% or 2.5% solution, these studies have also shown that using a 4.25% dextrose solution produce higher drained volumes than the 2.5% dextrose exchange [
Although differences in body mass composition (due to the majority of men in our sample or secondary to ethnic differences) can explain our results, the actual evidence regarding this issue is inconclusive. Previous investigations have shown the relationship between large body surface area and high D/P creatinine [
Although we did not determine any genetic factor that explains the variability among the three cohorts, several gene polymorphisms in the vascular endothelial growth factor (VEGF) gene, endothelial nitric oxide synthase gene (ENOS), and interleukin 6 (IL-6) gene have been correlated with the interpatient variability in PET results [
In this study there were no significant differences between age, gender, diabetes mellitus, serum albumin, C reactive protein, and the type of peritoneal transport, even when previous studies have revealed a higher proportion of men, diabetic patients, and low serum albumin concentration in the high transporter group [
Studies performed in other latitudes show different reference ranges for the classification of the types of peritoneal transport. The PET results of this study differ from the values described originally by Twardowski et al. and from other Latin American population. As a consequence of these discrepancies, we consider that CAPD prescription in our country should be made based on the presented reference values.
Our findings support the theory that different ethnical factors can be responsible for such variations and it validates the affirmation that each region should possess its own reference values.
Continuous ambulatory peritoneal dialysis
Peritoneal equilibration test.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors acknowledge their gratitude to the staff of the Dr. Luis Guillermo Brenes-Sobrado Nephrology Laboratory and to the registered nurses: Delia Gómez-Gómez and Carolina Méndez-Carvajal from the Chronic Ambulatory Peritoneal Dialysis Program of the San Juan de Dios Hospital, San José, Costa Rica.