PURPOSE:To define prospectively the volume of pleural fluid adequate for maximal yield of cytologic analysis of pleural fluid.
METHODS:Patients were eligible if they were to undergo diagnostic thoracentesis with malignancy in the differential diagnosis. Patients were enrolled prospectively. At time of thoracentesis, the first 50cc of fluid were put in a specimen cup and subsequent fluid was collected in a drainage bag. Both samples were sent for cytologic evaluation. The cytologist performing analysis was blinded as to which specimen was being evaluated.
RESULTS:Forty-four patients (21 m, 23 f, age 46 ± 11.1 years) were enrolled. Average volume of the “large volume” specimen was 890±375 ml (range 250-1800). 13 patients had no history of cancer. 31 had had a diagnosis of malignancy prior to thoracentesis, although malignant pleural involvement had never been documented for any. Breakdown of prior malignancies was 12 lung, 9 breast, 7 ovarian, 1 lymphoma, 1 pancreatic, and 1 adenocarcinoma of unknown primary.Cytology was positive for malignancy in 23 out of the 44 cases (55%). In the group of patients with an established history of cancer, the pleural fluid was positive for malignant cells in 19 of 33 samples (58%). In all 23 patients with malignant pleural effusion, both the 50cc specimen and the large volume specimen were cytologically identical. In all 21 patients with negative pleural cytology, there was again 100% concordance between 50cc samples and the larger samples.
CONCLUSION:The issue of minimum adequate pleural fluid volume for cytologic diagnosis has been a matter of protracted debate, but historically there has been little data to support opinion. The strongest data to date came from a retrospective 2002 study by Sallach et al. Our prospective study now unequivocally supports the concept that the submission of greater than 50cc of pleural fluid for cytologic analysis does not increase diagnostic yield.
CLINICAL IMPLICATIONS:If the goal of thoracentesis is to diagnose malignant pleural effusion, a 50cc sample will achieve maximal sensitivity.
DISCLOSURE:Wissam Abouzgheib, No Financial Disclosure Information; No Product/Research Disclosure Information