Pericardial fluid gram stain is a method of staining a sample of fluid taken from the sac surrounding the heart to diagnose a bacterial infection. The gram stain method is one of the most commonly used techniques for the rapid diagnosis of bacterial infections.

Your doctor may order this test if you have signs of a heart infection or a pericardial effusion with an unknown cause.

A sample of fluid will be taken from the sac surrounding the heart. Before this is done, some people may have a cardiac monitor to check for heart disturbances. Patches called electrodes are put on the chest, similar to during an ECG. You might have a chest x-ray or ultrasound before the test.

The skin of the chest is cleaned with antibacterial soap. A trained physician, often a cardiologist, inserts a small needle into the chest between the ribs and into the thin sac that surrounds the heart (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 placed in a very thin layer on a microscope slide. This is called a smear. A series of special stains are applied to the sample. This is called a gram stain. A laboratory specialist looks at the stained slide under the microscope, checking for bacteria.

The color, size, and shape of the cells help make it possible to identify the 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 should be able to give you pain medicine so that the procedure does not hurt very much.