A Minimum Volume of More Than 60 mL Is Necessary for Adequate Cytologic Diagnosis of Malignant Pericardial Effusions

Objectives: This study aims to determine the minimum pericardial fluid volume necessary for adequate cytologic diagnosis. Methods: We identified 480 pericardiocentesis specimens, divided them by volume into six bins, and calculated the malignancy fraction (percentage of malignant diagnoses) for each bin. We then combined bins at various cutoffs to determine a minimum threshold volume and evaluated their sensitivity. Results: The malignancy fraction increased from 6.5% for specimens 10 mL or less to 20.7% for more than 600 mL (P = .03). While the cumulative malignancy fraction was 18.1% above a cutoff of 60 mL, it was 10.6% below this threshold (P = .03). The sensitivity of cytology compared with pericardial biopsy was 70.0% for 60 mL or less and 91.1% for more than 60 mL (P = .14). Conclusions: Small-volume pericardiocentesis specimens detect fewer malignancies and have inferior sensitivity compared with pericardial biopsy. A volume of more than 60 mL should be submitted to cytology to ensure adequate diagnosis of pericardial fluids.