A specimen volume of ≥80 mL improves cytologic sensitivity for malignant ascites: a retrospective analysis of 2665...

Although paracentesis simultaneously allows cytologic evaluation of peritoneal fluid and symptomatic relief, its utility is limited by a paltry 50% to 60% sensitivity for malignancy. Specimen volume has recently been shown to affect cytologic diagnosis in other body fluids, but its role has never been examined in ascites. This study evaluates how specimen volume impacts cytologic diagnosis of malignant ascites.

We identified 2665 consecutive paracentesis specimens with documented numeric volumes collected at our institution between 1994 and 2013. We separated the cases into 10 bins of roughly equivalent sample size and compared the percentage of cases that received malignant diagnoses across each cutoff volume. When follow-up pathology was available, we also compared the sensitivity of cytology with the gold standard of surgical pathology.

The peritoneal fluids had a mean volume of 760.2 mL (range: 1-10,000). Just 11.3% of specimens with volumes <80 mL were diagnosed as malignant, while 20.1% were malignant at volumes ≥80 mL (P < 0.001, OR = 0.51, 95% CI = 0.39-0.64). Lower volume specimens also had more indeterminate and nondiagnostic results. Cytologic sensitivity increased from 56.7% for specimens <80 mL to 75.4% for volumes ≥80 mL (P = 0.03, OR = 0.43, 95% CI = 0.19-0.94).

A specimen volume of ≥80 mL is associated with increased cytologic sensitivity for malignant ascites and a higher rate of malignant diagnoses. The disparate sensitivity at lower volumes likely stems from inadequate sampling of larger specimens. Although fluids should not be summarily rejected based on volume, a specimen volume of ≥80 mL minimizes the influence of specimen size on diagnostic adequacy in paracentesis specimens.