The optimal volume of pleural fluid to make the diagnosis of a malignant effusion is unknown. The purpose of our study was to demonstrate if a minimum volume of pleural fluid (10 mL) is as good as a large volume thoracentesis to make a cytopathological diagnosis of malignancy.
121 diagnostic thoracentesis samples were obtained from 102 patients (42 men and 60 women) with suspected or known malignant pleural effusions. Pleural fluid from each patient was collected in three aliquots for cytological examination (10mL, 60mL, ≥ 150mL). The pathologist was blinded to all patient identifiers and to the aliquot volume. Sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) was calculated for each pleural fluid volume for the diagnosis of malignancy.
Pleural malignancy was diagnosed in 61 pleural fluid samples (50.4 %). For direct smear/cytospin evaluation, there was increased sensitivity and NPV for 60 mL as compared to 10 mL (p= 0.012 and p= 0.045, respectively) and for 150 mL as compared to 10 mL (p= <0.001 and p= 0.009, respectively). When using combined direct smear/cytospin and cell block preparations, statistical significance for sensitivity and NPV existed between the 10 mL and 150 mL specimens (p= 0.031 and p= 0.033, respectively). No statistical difference existed for specificity or PPV for any of the aliquot volumes.
The sensitivity for diagnosis of pleural malignancy is dependent on the pleural fluid volume extracted during thoracentesis. When using combined direct smear/cytospin and cell block preparations, ≥ 150 mL of pleural fluid performed better than smaller volumes to make the cytopathologic diagnosis of malignancy.
Large volume thoracentesis should be obtained from patients with a suspected malignant pleural effusion to make the cytopathologic diagnosis of malignancy.
Jennifer Swiderek, No Financial Disclosure Information; No Product/Research Disclosure Information