Reproducibility of the peritoneal equilibration test in CAPD patients

Peritoneal equilibration testing: Your questions answered

The peritoneal equilibration test (PET), first described in 1987, is a semiquantitative assessment of peritoneal transfer characteristics in patients undergoing peritoneal dialysis. It is typically performed as a 4-h exchange using 2.27/2.5% dextrose dialysate with serial measurements of blood and dialysate creatinine, urea, and glucose concentrations. The percentage absorption of glucose and D/P creatinine ratio are used to determine peritoneal solute transfer rates. It is used to both help guide peritoneal dialysis prescriptions and to prognosticate. There are several derivative tests which have been described in the literature. In this review, we describe the original PET, the various iterations of the PET, the information gleaned, and the use in the setting of poor solute clearance and in the diagnosis of membrane dysfunction, and limitations of the PET.

Baseline Peritoneal Membrane Transport Characteristics Are Associated with Peritonitis Risk in Incident Peritoneal Dialysis Patients

The peritoneal equilibration test (PET) is a semi-quantitative measurement that characterizes the rate of transfer of solutes and the water transfer rate across the peritoneum in patients treated with peritoneal dialysis (PD). The results of the PET are used to maximize daily peritoneal ultrafiltration and solute clearances. Previous studies have shown that high transport status is associated with ultrafiltration failure, malnutrition, and reduced survival; however, the way in which peritoneum transport characteristics affect peritonitis risk is unknown. In the current cohort study, we recruited 898 incident-PD patients and used intention-to-treat analysis to test if baseline PET affected the subsequent 3-year peritonitis rate. Among all recruited PD patients, 308 (34.2%) developed peritonitis within three years. Multivariate Cox regression analysis showed that the high-transport group has the greatest peritonitis risk (HR 1.98, 95% CI: 1.08–3.62) even after an adjustment for demographics, comorbid diseases, and biochemical measurements. We concluded that a baseline high peritoneal membrane transport rate is an independent risk factor for peritonitis in incident PD patients.

Longitudinal Study of Peritoneal Membrane Function in Continuous Ambulatory Peritoneal Dialysis: Relationship with Peritonitis and Fibrosing Factors

Background

The peritoneal equilibration test (PET) is a useful assessment of peritoneal function in continuous ambulatory peritoneal dialysis (CAPD) patients. However, the natural course of longitudinal change in peritoneal transport is not well defined.

Patients

We studied 105 unselected CAPD patients. Average age at enrollment was 50.7 ± 11.3 years.

Methods

A PET was performed at enrollment. Peritoneal transport was expressed as dialysate-to-plasma creatinine ratio at 4 hours (D/P). Fibrosing factors and mesothelial cell markers, including TGFJJ, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), hyaluronan, and cancer antigen 125 (CA125), were measured in overnight peritoneal dialysate effluent (PDE). Patients were followed for two years. Peritonitis episodes were recorded. Severe peritonitis was defined as an episode that required catheter removal or antibiotic therapy for more than 3 weeks. After two years, 75 patients were still alive and on CAPD.

Results

The PET was repeated in 64 patients, of whom 35 were male and 9 had diabetes. The change in D/P over two years was represented as ΔD/P. No significant change in peritoneal transport was seen after two years (D/P: 0.56 ± 0.12 vs 0.55 ± 0.13). A centripetal pattern of change in D/P was observed. The ΔD/P had normal distribution and was inversely correlated with D/P at baseline ( r = -0.427, p < 0.005). Both results suggest a regression-to-mean phenomenon. The ΔD/P had no significant correlation with the total number of peritonitis episodes (Spearman r = 0.052, p = 0.74), but after severe peritonitis, affected patients had higher ΔD/P than patients who experienced no severe infection (0.040 ± 0.136 vs -0.032 ± 0.120, p < 0.05). For patients with no episodes of severe peritonitis (n = 47), ΔD/P was weakly correlated with baseline TGFβ level ( r = -0.506, p < 0.01). No correlation was seen between the levels of other fibrosing factors and change in peritoneal transport.

Conclusions

Our findings suggest that the centripetal change of peritoneal transport probably reflects a regression-to-mean phenomenon. Peritoneal transport increases after severe peritonitis. The role of TGFβ levels in PDE with regard to longitudinal change in peritoneal transport requires further study.

Unraveling Hepcidin Plasma Protein Binding: Evidence from Peritoneal Equilibration Testing

Peptide hormone hepcidin regulates systemic iron metabolism and has been described to be partially bound to α2-macroglobulin and albumin in blood. However, the reported degree of hepcidin protein binding varies between <3% and ≈89%. Since protein-binding may influence hormone function and quantification, better insight into the degree of hepcidin protein binding is essential to fully understand the biological behavior of hepcidin and interpretation of its measurement in patients. Here, we used peritoneal dialysis to assess human hepcidin protein binding in a functional human setting for the first time. We measured freely circulating solutes in blood and peritoneal fluid of 14 patients with end-stage renal disease undergoing a peritoneal equilibration test to establish a curve describing the relation between molecular weight and peritoneal clearance. Calculated binding percentages of total cortisol and testosterone confirmed our model. The protein-bound fraction of hepcidin was calculated to be 40% (±23%). We, therefore, conclude that a substantial proportion of hepcidin is freely circulating. Although a large inter-individual variation in hepcidin clearance, besides patient-specific peritoneal transport characteristics, may have affected the accuracy of the determined binding percentage, we describe an important step towards unraveling human hepcidin plasma protein binding in vivo including the caveats that need further research.

Clinical characteristics of dialysis related sclerosing encapsulating peritonitis: multi-center experience in Korea

Sclerosing encapsulating peritonitis (SEP) is a rare but serious complication in patients with continuous ambulatory peritoneal dialysis (CAPD), and is characterized by a progressive, intra-abdominal, inflammatory process resulting in the formation of sheets of new fibrous tissue, which cover, bind, and constrict the viscera, thereby compromising the motility of the bowel. No satisfactory estimate is available on the comparative incidence of dialysis related SEP and the pathogenesis of SEP still remains uncertain. Although recent therapeutic approaches have reported varying degrees of success, an efficient measure to detect, at an early stage, patients at risk for SEP would be beneficial and a standardized treatment regimen to prevent the illness is urgently needed. This study aimed to evaluate the clinical features of SEP and to identify the possible risk factors for the development of SEP in CAPD patients. We retrospectively reviewed by questionnaire SEP cases among CAPD patients from 7 university hospital dialysis centers in Korea, including Yonsei University, Ajou University, Catholic University, Inha University, Kyungpook University, Seoul National University and Soonchunhyang University, from January 1981 to December 2002. Out of a total of 4,290 CAPD patients in these centers, 34 cases developed SEP with an overall prevalence of 0.79%. The male to female ratio was 17:17. The median age of these patients was 44.5 years (range 19-66). The median duration of CAPD before SEP was 64 months (9-144) and 68% of patients (23/34) had been on CAPD for more than 4 years. Peritonitis (including two fungal cases) was the main cause of catheter removal in SEP (27 cases, 79%). Seventy-five percent of the cases (15/20) were administered beta-blocker for a mean duration of 85 months (26-130). Among 10 cases with available peritoneal equilibration test (PET) data, 8 showed high transporter characteristics, and the remaining 2 were high average. Eighteen cases were diagnosed by clinical and radiologic methods, and 16 were surgically diagnosed. Eleven cases were surgically treated and the others were treated conservatively with intermittent total parenteral nutrition (TPN). The overall mortality rate was 24%. SEP is a serious, life threatening complication of CAPD. Most cases had a PD duration of more than 4 years, a history of severe peritonitis, and high transporter characteristics in PET. Therefore, to reduce the incidence of SEP, careful monitoring and treatment, including early catheter removal in patients with severe peritonitis, should be considered for long-term CAPD patients with the above characteristics.

Comparison of peritoneal equilibration test with 99mTc-DTPA excretion in the assessment of peritoneal permeability

Assessment of peritoneal permeability is necessary for successful management of end-stage renal disease (ESRD) patients by continuous ambulatory peritoneal dialysis (CAPD). The objective of this study was to develop an alternative method of assessing the peritoneal permeability and to compare this method with the conventional method, the peritoneal equilibrium test, first described by Twardowski in 1987. Twenty patients undergoing regular CAPD were included in this study. Before starting the peritoneal dialysis, 370 MBq (10 mCi) technetium-99m diethylene triamine penta-acetic acid ((99m)Tc-DTPA) was injected intravenously. A standard dose of the same quantity was kept and used later for calculations. At the end of 4 h, a dialysate fluid sample (1 ml) was collected and the total dialysis effluent fluid volume was measured. Excretion of (99m)Tc-DTPA into the dialysate fluid as a percentage of the injected dose was calculated. Simultaneously, standard peritoneal equilibrium test values were recorded for comparison. Peritoneal excretion of (99m)Tc-DTPA ranged from 8% to 25% of the injected dose, depending on the peritoneal membrane permeability. When the results were compared with the conventional method, a good correlation (r=0.79) was found. This innovative radionuclide technique is a simple and convenient method to assess the peritoneal membrane permeability and can be used as an alternative to the peritoneal equilibrium test, which is very cumbersome and associated with many limitations.

Peritoneal transport properties and dialysis dose affect growth and nutritional status in children on chronic peritoneal dialysis. Mid-European Pediatric Peritoneal Dialysis Study Group

To evaluate a possible effect of peritoneal transport properties and dialysis dose on the physical development of children on chronic peritoneal dialysis, a cohort of 51 children was prospectively followed for 18 mo. Peritoneal transport characteristics were assessed by serial peritoneal equilibration tests (PET), dialysis efficacy by dialysate and residual renal clearance measurements, and growth and nutritional status by the longitudinal changes (delta) of height SD score (SDS), body mass index (BMI) SDS, and serum albumin. delta height SDS was negatively correlated with the creatinine equilibration rate observed in the initial PET (r = -0.31, P < 0.05). Multiple regression analysis confirmed the negative effect of the high transporter state (partial r2 = 0.07), and disclosed an additional positive effect of dialytic C(Cr) (partial r2 = 0.11) and a weak negative effect of daily dialysate volume (partial r2 = 0.04) on delta height SDS. delta BMI SDS was strongly age-dependent (r = -0.48, P < 0.001); while relative body mass gradually increased below 4 yr of age, it remained stable in older children. Positive changes in BMI SDS were associated with rapid PET creatinine equilibration rates (univariate r = 0.35, P < 0.05) and/or large dialysate volumes (multivariate partial r2 = 0.11), suggesting a role of dialytic glucose uptake in the development of obesity. The change in serum albumin concentrations was positively correlated with dialysate volume (partial r2 = 0.14), and negatively affected by dialytic protein losses (partial r2 = 0.06). In conclusion, the peritoneal transporter state is a weak but significant determinant of growth and body mass gain in children on chronic peritoneal dialysis. Rapid small solute equilibration contributes to impaired growth but enhanced acquisition of body mass. Dialytic small solute clearance has a weak positive effect on statural growth independent of the transporter state, but does not affect body mass gain.

Evaluation of ultrafiltration failure

The evaluation of ultrafiltration failure is embarked upon when a patient has persistent problems with symptoms and signs of fluid overload. Fluid overload is a common problem in peritoneal dialysis (PD) patients and the risk of its occurrence increases with time on dialysis. Although often attributed to changes in peritoneal membrane function (membrane failure), there are a number of potential, and frequently more common factors that can contribute to the failure of adequate fluid removal in patients on PD. Many of the causes of ultrafiltration failure may be apparent after an initial informal evaluation. However, if after this the etiology remains unexplained, a systematic approach to the differential diagnosis of this problem can be utilized with the use of the peritoneal equilibration test. Once a diagnosis is confirmed, a logical therapeutic plan can be formulated.