To determine PD-related peritonitis in the end-stage kidney disease patients undergoing CAPD, we excluded patients who had previous peritonitis. After follow-up for 3 years, the ratio of peritonitis in our study was 15.8% (Table 1). There have been some reports about the prevalence of PD-related peritonitis. Ye H. et al.  conducted a study with 1321 PD patients with a follow-up of 5 years, and the ratio of peritonitis was 28.16% (372/1321 patients). Furthermore, in the first year of PD initiation, 169 (13%) patients had experienced episodes of peritonitis, and the proportion of patients with peritonitis fluctuated from 8% to 13% in the subsequent years. Gadola L. et al.  surveyed the rate of peritonitis in 222 PD patients with a follow-up of 6 years, and the results showed 95 patients suffered 1 or more episodes of peritonitis (42.79%). In a study by Ponce, the ratio of peritonitis in children was 25.45% with a follow-up of 7 years (125 first episodes of peritonitis in 491 PD patients who were children) . The ratio of peritonitis in our study was lower than that in other studies, because our follow-up time was shorter. Overall, 27.3% of patients had a positive bacterial culture in our study, which is similar to other study results [5, 21].
Relation between peritonitis and some patient characteristics
In Vietnam, peritoneal dialysis is concentrated only in 2 large cities, Hanoi and Ho Chi Minh City. When being recommended chronic kidney replacement therapy, most patients choose maintenance hemodialysis. Only approximately 20% of patients choose peritoneal dialysis, because they do not have time to go to hemodialysis centers. When comparing the peritonitis and nonperitonitis groups, we found some patient characteristics related to peritonitis. In the peritonitis group, the average age was older and the ratios of low education and DM were significantly higher than those in the nonperitonitis group (p< 0.001) (Table 1). It remains controversial whether older PD patients have a substantially increased risk of peritonitis than their younger counterparts. More recently, retrospective studies have found that older age (more than 65 years) was the only identifiable risk factor associated with peritonitis [22,23]. It seems highly probable that touch contamination and bowel dysfunction are important underlying causes of episodes of peritonitis in older PD patients . Diabetes mellitus and low education have been risk factors for PD-related peritonitis in previous studies [24-26]. As diabetes mellitus is regarded a risk factor for infections in general, it seems reasonable to also consider it a risk factor for peritonitis in PD patients . In this study, we found the relationship between peritonitis and overhydration (Table 1,2). The results of our study were similar to those of others [13, 14]. The association between OH and peritonitis maybe by enteric microorganisms . This seems to be reasonable, as there is a trend toward an association between baseline levels of C-reactive protein and PD-related peritonitis (Table 1,2).
The relationship between peritonitis and malnutrition was also expressed in our study (Table 1,2). The average serum albumin and prealbumin levels in the peritonitis group were significantly lower than those in the nonperitonitis group (p< 0.001). Peritoneal dialysis itself might lead to protein-energy wasting due to the continuous glucose absorption from peritoneal dialysis solutions and abdominal fullness induced by the dialysate. The result is a decrease in serum albumin and prealbumin concentrations in patients with peritoneal dialysis . Dong J et al. also confirmed that protein leakage predicted the risk for peritonitis in patients on peritoneal dialysis, and this association remained even after adjustment for systemic inflammation estimated by serum albumin, hs-CRP, and IL-6 .
Factors predicting peritonitis
In this study, we found that there were many independent factors related to peritonitis in CAPD patients, of which prealbumin and OH are closely related (p< 0.001) (Table 2). We also found that OH and serum prealbumin were the independent predictors of peritonitis compared to other factors, such as hemoglobin, serum albumin, and hs-CRP (AUC of prealbumin was 0.838 and that of OH was 0.851, p< 0.001) (Figure 1). The predictive values, by Kaplan-Meier analysis, for both serum prealbumin and OH with regard to peritonitis were also evident with a follow-up of 3 years (Figure 2,3). There are some previous reports about predictive factors for PD-related peritonitis in CAPD patients [20, 22, 23]. Gadola L. et al.  confirmed that a multidisciplinary peritoneal educational program improved peritonitis rates, independently of other risk factors. Okayama M. et al. found that aging was an important risk factor for peritoneal dialysis-associated peritonitis . In particular, Kerschbaum J et al.  reviewed 415 studies on risk factors for peritonitis in PD patients. From those studies, the author found that the risk factors for peritonitis were divided into two groups: nonmodifiable and modifiable risk factors. Nonmodifiable risk factors are ethnicity, old age, female, cardiovascular comorbidities, DM, underlying renal disease (such as lupus), and loss of residual renal function. Modifiable risk factors are malnutrition, overweight, smoking, comedication with immunosuppressants, depression, and low socioeconomic status. In summary, many risk factors for PD-related peritonitis have been identified in studies of acceptable methodological quality. Overhydration is common among PD patients and related to cardiovascular risk and death [29-31]. Prealbumin levels were an independent and sensitive predictor for mortality in incident PD patients, showing a good correlation with nutritional and inflammatory markers [17, 32]. An association between OH and the risk of peritoneal infection by enteric germs was reported in a study by Carvalho Fiel D . It has been suggested that persistent edema of the intestinal wall may favor microbial and bacterial endotoxin transmigration, leading to systemic infections (including peritonitis) in some cases . Serum albumin and prealbumin are the measures to evaluate the nutritional status of chronic patients in general, especially in patients receiving peritoneal dialysis. Decreased albumin and prealbumin concentrations associated with peritonitis in peritoneal dialysis patients have been mentioned by several authors [26-28]. It might be hypothesized that hypoalbuminemia (as a result of malnutrition, the inflammatory response, or uremia itself) may lead to a higher susceptibility to infection . Thus, both OH and serum prealbumin are modifiable risk factors for PD-related peritonitis, which have predictive value for peritonitis in CAPD patients. This result once again confirms the role of OH and serum prealbumin in predicting outcomes of CAPD patients. From this result, good control of OH and serum prealbumin is needed to reduce the rate of peritonitis in CAPD patients.
Although our results showed that overhydration and low serum prealbumin were the independent predictors of PD-related peritonitis in CAPD patients, this study still had some limitations. First, we did not determine evidence of all other modifiable and nonmodifiable factors related to peritonitis among PD patients . As a result, we could not determine the "real" association of prealbumin and OH with the outcome. Second, we were unable to obtain repeated measures of prealbumin and OH during the 3-year follow-up period.