A sample of fluid will be taken from the pericardium. This is done with a procedure called pericardiocentesis. Before this is done, you may have a heart monitor to check for heart problems. Patches called electrodes are put on the chest, similar to during an electrocardiogram (ECG). You will have a chest x-ray or ultrasound before the test.

The skin of the chest is cleaned with antibacterial soap. Your doctor (usually a cardiologist or radiologist) then inserts a small needle into the chest between the ribs and into the pericardium. A small amount of fluid is taken out.

You may have an ECG and chest x-ray after the procedure. Sometimes, the pericardial fluid is taken during open heart surgery.

A drop of the pericardial fluid is spread in a very thin layer on a microscope slide. This is called a smear. The specimen is stained with crystal violet stain and goes through more processing before it is examined under the microscope for bacteria.

The characteristic appearance of the bacteria, such as their color, shape, clustering (if any), and pattern of staining help determine the type of bacteria.

You will be asked not to eat or drink anything for several hours before the test. A chest x-ray or ultrasound may be done before the test to identify the area of fluid collection.

You will feel pressure and some pain as the needle is inserted into the chest and when the fluid is removed. Your doctor will likely give you pain medicine so that the procedure is not too uncomfortable.

Your health care provider may order this test if you have a heart infection (myocarditis), signs of a heart sac infection (pericarditis), or a pericardial effusion (fluid buildup of the pericardium) with an unknown cause.

A normal result means no bacteria are seen in the stained fluid sample.

If bacteria are present on the Gram stain, you may have an infection of the pericardium or heart. Blood tests and bacterial culture can help identify the specific organism causing the infection.

Complications are rare but may include:

• Heart or lung puncture
• Infection

Gram stain of pericardial fluid

LeWinter MM, Cremer PC, Klein AL. Pericardial diseases. In: Libby P, Bonow RO, Mann DL, Tomaselli GF, Bhatt DL, Solomon SD, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12th ed. Philadelphia, PA: Elsevier; 2022:chap 86.

Malick WA. Pericarditis and pericardial effusions. In: Leppert BC, Kelly CR, eds. Netter's Integrated Review of Medicine: Pathogenesis to Treatment. Philadelphia, PA: Elsevier; 2021:chap 61.

Updated by: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.