What is being tested?

Pericardial fluid is a liquid that acts as a lubricant for the movement of the heart. It is found in small quantities between the two layers of the pericardium. Pericardial fluid is produced by mesothelial cells in the membranes and acts to reduce friction as the heart pumps blood.

A variety of conditions and diseases can cause inflammation of the pericardium (pericarditis) and/or excessive accumulation of pericardial fluid (pericardial effusion) for example; inflammation, congestive heart failure, autoimmune disorders or metastatic cancer.

Pericardial fluid analysis comprises a group of tests used to determine the cause: red and white blood cell counts and differential, cytology, Gram stain, fungal culture and acid fast staining for tuberculosis. Biochemical tests that may be performed are pH, glucose, lactate dehydrogenase (LD) and total protein.

How is it used?

Pericardial fluid analysis is sometimes used to help diagnose the cause of inflammation of the pericardium called pericarditis and/or fluid accumulation around the heart (pericardial effusion). However, just as important for diagnosis are the ECG, echocardiography, blood markers of inflammation (CRP, ESR, white blood cell count), troponin (myocardial damage) and chest X-ray or CT scan.

When is it requested?

Pericardial fluid analysis is indicated if there is suspicion of tuberculous, purulent or neoplastic pericarditis and large or symptomatic effusions refractory to medical treatment. Pericardial fluid removed for therapeutic reasons (pericardial tamponade) is often routinely sent for analysis.

What does the result mean?

Microscopic examination - Normal pericardial fluid has small numbers of white blood cells (WBCs) but no red blood cells (RBCs) or microorganisms. Laboratories may examine drops of the pericardial fluid and/or use a special centrifuge (cytocentrifuge) to concentrate the fluid’s cells at the bottom of a test tube. Samples are placed on a slide, treated with special stain, and an evaluation of the different kinds of cells present is performed.

• Total cell counts - quantity of WBCs and RBCs in the sample. Increased WBCs may be seen with infections and other causes of pericarditis.
• WBC differential - determination of percentages of different types of WBCs. An increased number of neutrophils may be seen with bacterial infections.
• Cytology - a cytocentrifuged sample is treated with a special stain and examined under a microscope for abnormal cells. This may be done when a mesothelioma or metastatic cancer is suspected. The presence of certain abnormal cells, such as tumour cells or immature blood cells, can indicate what type of cancer is involved.

Infectious disease tests - routine tests for microorganisms if infection is suspected:

• Gram stain - for direct observation of bacteria or fungi under a microscope. There should be no organisms present in pericardial fluid.
• Bacterial culture and susceptibility testing - ordered to detect any microorganisms, which will grow in the culture. If bacteria are present, susceptibility testing can be performed to guide antimicrobial therapy. If there are no microorganisms present, it does not rule out an infection; they may be present in small numbers or their growth may be inhibited because of prior antibiotic therapy.
• Depending on pretest probability, fungal culture and Acid fast bacilli (AFB) testing for tuberculosis. 

Is there anything else I should know?

Increased amounts of pericardial fluid can restrict the movement of the heart. Cardiac tamponade is a condition that reflects pericardial fluid buildup to the point that pressure on the heart prevents it from filling normally. Rapid fluid build-up can be a medical emergency, causing heart failure and death. When fluid accumulates slowly, the pericardial sac stretches and symptoms gradually worsen.

Common questions

• What is pericardiocentesis and how is it performed?

Pericardiocentesis is the removal of pericardial fluid from the pericardial sac with a needle and syringe. An intravenous (IV) line may be started and the person may be given medications prior to the sample collection. The patient is positioned lying down. A local anaesthetic is applied, then the doctor inserts the needle into the space between the ribs (fifth to sixth intercostals space) on the left side of the chest and into the pericardial sac and removes a fluid sample. An ultrasound scan may be used to help guide the needle.

Pericardiocentesis is lifesaving in cardiac tamponade, which is the usual reason it is done although sometimes it is performed for diagnosis. Ideally pericardiocentesis, guided by ultrasound is done in a cardiac catheterisation laboratory with ECG monitoring but in emergency situations it can be performed at the bedside.

More information

RCPA Manual: Pleural/pericardial fluid examination