How Much Pleural Fluid Should Be Sent for Cytology?

When patients with suspected malignant pleural effusion undergo diagnostic thoracentesis, what volume of fluid should be sent to the lab for cytologic diagnosis? In this prospective study, researchers identified 102 patients with suspected (94) or known (8) malignant effusions who underwent 121 thoracenteses. From each thoracentesis, three aliquots of pleural fluid (10 mL, 60 mL, and ≥150 mL) were sent for analysis. Ultimately, malignancies (mainly lung and breast cancers) were diagnosed in 88% of patients.

Sensitivities for diagnosis of malignancy by direct smear/cytospin for 10-mL, 60-mL, and ≥150-mL fluid samples were 49%, 63%, and 69%, respectively. The difference in sensitivity between 150 mL and either smaller volume was significant. W…