Pleural fluid smear

The pleural fluid smear is a screening test for the presence of microorganisms or abnormal cells in pleural fluid in the space around the lungs.

How the test is performed
A sample of pleural fluid is examined under the microscope. If organisms are detected by smear, other methods to specifically identify them may be performed.

How to prepare for the test
It is important not to cough, breathe deeply, or move when the fluid sample is being taken. There is no other special preparation for the test.

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

How the test will feel

The specimen is obtained by thoracentesis (a needle aspiration of fluid in the pleural space). An area on the chest is cleansed with antibacterial soap and numbed with local anesthetic. A needle is placed between the ribs, and a sample of fluid is withdrawn from the chest.

You may feel a stinging sensation when the anesthetic in injected. You may feel some pressure and slight localized pain when the thoracentesis needle enters the pleural space. A Chest x-ray is usually done following the test to be sure the lung tissue was not affected by the test.

Why the test is performed
The test is performed when infection of the pleural space is suspected, or when an abnormal collection of pleural fluid is noticed by Chest x-ray.

Normal Values

Normally, no organisms are present in the pleural fluid.

What abnormal results mean

Positive results may indicate that microorganisms or cancer cells are present. Other tests can help identify the specific type of infection or cancer.

What the risks are

There is a risk of internal bleeding into the lung and Pneumothorax (collapsed lung). Serious complications are extremely rare.

Special considerations

The fluid smear cost and the cost of the procedure to obtain the specimen are charged separately. Other tests may be done on the sample of fluid obtained.


Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

Medical Encyclopedia

  A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0-9

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.