An investigation of adequate volume for the diagnosis of malignancy in pleural fluids

The cytological examination of pleural effusions is an important investigation in the diagnosis of malignancy. Maximizing the chances of identifying malignant effusions is therefore desirable. Recent Royal College of Pathologists guidelines, based on the British Society for Clinical Cytology codes of practice, have suggested that a minimum of 20 ml of pleural fluid is required for diagnostic purposes.

We examined 2155 pleural fluids received over a 6-year period in order to define a minimum required volume for adequacy. By examining the plateau phase of a graph of threshold volumes for initial samples received for each patient (n =1584) we determine that a minimum fluid volume of 25 ml is required and that more than 50 ml does not improve sensitivity.

Between 25 and 50 ml of fluid are required for the adequate assessment of pleural effusions for malignancy.