Determination of the optimal volume of ascitic fluid for the precise diagnosis of malignant ascites

Background/Aims: The aim of this study was to determine the optimal volume of peritoneal effusion required to diagnose malignant ascites. Patients and Methods: The authors recruited 123 patients with shifting dullness and obtained 123 peritoneocentesis fluid samples. The samples were divided into seven aliquots of 10, 50, 100, 150, 200, 250, and 300 mL for cytopathological examination. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) were calculated for each aliquot. Results: The sensitivity for the diagnosis of malignant ascites gradually increased as the sample volume increased and reached a constant value at a volume of 200 mL. The sensitivity and NPV for the 10-, 100-, and 150-mL volumes were significantly different from those for the 200-mL sample. However, the sensitivity and NPV for the 250- and 300-mL volumes were not significantly different. The sensitivity for the diagnosis of malignant ascites is closely related to the volume of peritoneal fluid that is extracted by peritoneocentesis. Conclusion: We suggest a volume of 200 mL as the optimal minimum volume to confirm alignant ascites in patients with shifting dullness.