A cytology exam of pleural fluid is a laboratory test to detect cancer cells and certain other

cells in the area that surrounds the lungs. This area is called the pleural space. Cytology

means the study of cells.The purpose of testing pleural fluid is to determine the cause of a

pleural effusion. A pleural effusion occurs when excess fluid collects in the area between

the lungs and the tissue that covers the lungs, known as the pleural space.