Characteristics of Pancreatic Cancer-associated Ascites and Redefined Criteria for Bacterial Peritonitis.

OBJECTIVES

The diagnosis of spontaneous bacterial peritonitis relies on polymorphonuclear (PMN) cell counts (>250/mm 3 ) in cirrhotic ascites. However, ascites in pancreatic ductal adenocarcinoma (PDAC) develop through mixed mechanisms, presenting different profiles compared with those of cirrhotic ascites. This study aimed to investigate the characteristics of PDAC-associated ascites and propose redefined criteria for bacterial peritonitis diagnosis in patients with PDAC.

METHODS

This retrospective study was conducted at 3 tertiary medical centers in Korea. The etiology (peritoneal carcinomatosis, portal hypertension, or mixed etiology) and characteristics of PDAC-associated ascites of the exploration cohort (n=493) were analyzed. Diagnostic criteria for bacterial peritonitis were then derived from patients with elevated PMN cell counts (>250/mm 3 , n=183) in ascites. Subsequently, these criteria were validated in an external cohort (n=614).

RESULTS

Peritoneal carcinomatosis and portal hypertension showed similar proportions as ascites etiologies. Median PMN cell counts and proportions were higher in peritoneal carcinomatosis (106/mm 3 , 13%) than in portal hypertension (15/mm 3 , 7%; P <0.001) and mixed etiology (38/mm 3 , 9%; P <0.05). In the derivation analysis, PMN cell proportion was the sole statistically significant variable for bacterial peritonitis diagnosis, with an optimal cutoff value of >35.5%. The redefined diagnostic criteria for bacterial peritonitis (PMN cell proportion >35% with counts >250/mm 3 ) increased the specificity from 85% to 92% (RR: 1.08, 95% CI: 1.04-1.13, P <0.001) in external validation, with minimal compromise in the sensitivity.

CONCLUSIONS

PDAC-associated ascites exhibited distinct characteristics according to their etiology. Redefined diagnostic criteria could aid in a more specific diagnosis of bacterial peritonitis in patients with PDAC.