A sample of pleural fluid is obtained by a procedure called thoracentesis. The specimen is examined for chemical content, cellular composition, the presence of malignant cells, and the presence of microorganisms.

There is no special preparation. Do not cough, breathe deeply, or move during the test to avoid injury to the lung. A chest x-ray may be performed before or after the test. Your doctor will probably want to observe you for 30-60 minutes after the procedure to see if a complication occurs.

You will be positioned sitting on the edge of a chair or bed with your head and arms resting on a table. The skin around the insertion site is disinfected, and the area is draped. A local anesthetic is injected into the skin.

The thoracentesis needle is inserted above the rib into the pocket of fluid. There will be a stinging sensation when the local anesthetic is injected, and a sensation of pressure when the needle is inserted into the pleural space. Inform your health care provider if you develop sharp chest pain or shortness of breath.

The test is performed to determine the cause of a pleural effusion.

With normal values, the pleural cavity contains less than 20 milliliters (four teaspoons) of serous (clear, yellowish) fluid.

With abnormal results, the analysis of the fluid will indicate possible causes of pleural effusion, such as infection, neoplasms, heart failure, and cirrhosis. If infection is suspected, a culture of the fluid is done to determine the presence of microorganisms.

Another condition under which the test may be performed is hemothorax, a collection of blood in the pleura.

The risks of thoracentesis are pneumothorax (collapse of the lung), fluid re-accumulation, pulmonary edema, excessive loss of blood, infection, and respiratory distress. Serious complications are uncommon.

The fluid analysis cost and the cost of the procedure to obtain the specimen are charged separately.