Diagnostic Usefulness of Carbohydrate Antigen-125 in Cancerous and Noncancerous Peritoneal Effusions

Carbohydrate antigen-125 (CA-125) is a tumor marker that has been used for differential diagnosis of peritoneal malignancies. The aim of the present study was to evaluate the diagnostic usefulness of simultaneous quantification of CA-125 in peritoneal fluid and serum for abdominal cancer cases and noncancer diseases. Noncancer disease group included cirrhotic patients (n = 28) and spontaneous bacterial peritonitis (SBP) patients (n = 11). Abdominal cancer group was composed of histologically diagnosed various malignancies (n = 10), such as gastric cancer. CA-125 levels were quantified by chemiluminescent enzyme immuno-assay. Diagnostic usefulness tests and receiver operating characteristics (ROC) curve analysis were performed for the levels of peritoneal fluid CA-125 (pCA-125) and serum CA-125 (sCA-125), and the ratio of pCA-125 to sCA-125 (p/sCA-125). The sCA-125 levels were significantly higher in noncancer patients than those in the cancer patients, while the pCA-125 levels showed no significant difference between the two groups. Notably, the p/sCA-125 ratio was significantly lower in the noncancer patients than that in the cancer patients. Area under the ROC curve was 0.267 for sCA-125, 0.542 for pCA-125 and 0.831 for p/sCA-125. The accepted cutoff values were the combination of values that gave the greatest diagnostic sensitivity plus specificity. Either sCA-125 or pCA-125 value gave lower diagnostic accuracy, whereas p/sCA-125 value demonstrated a significantly higher diagnostic accuracy (sensitivity-specificity pairs: 0.40-0.33 for sCA-125, 0.60-0.54 for pCA-125, and 0.80-0.72 for p/sCA-125, respectively). Hence, determination of p/sCA-125 improves the biochemical discrimination of abdominal cancerous cases from noncancerous diseases.