Pericardial Fluid Analysis

Pericardial fluid analysis is used to help diagnose the cause of inflammation of the pericardium (pericarditis) and/or fluid accumulation around the heart (pericardial effusion). An initial set of tests (protein or albumin, cell count and appearance) is used to differentiate between the two types of fluid that may be produced (transudate and exudate). Additional tests on the fluid itself may be used to help distinguish possible conditions causing an exudate: 

• Infectious diseases - caused by viruses, bacteria, or fungi. Infections may originate in the pericardium or spread there from other places in the body. For example, pericarditis may follow a respiratory infection. Viral infection is the most common. 
• Bleeding -  bleeding disorders and/or trauma can lead to blood in the pericardial fluid. 
• Inflammatory conditions - pericarditis may follow a heart attack, radiation treatment, or be part of autoimmune disorders such as rheumatoid arthritis and systemic lupus erythematosus. Hypersensitivity or post-infectious inflammation may also be a cause. 
• Cancer - such as mesothelioma in the pericardium or metastatic cancer that has spread to it. 

Pericardial fluid analysis may be requested when a doctor suspects that a patient has a condition or disease that is causing pericarditis and/or pericardial effusion. It may be used when a patient has some combination of the following signs and symptoms: 

• Chest pain, sharp or sometimes dull, that may be relieved by bending forward 
• Coughing 
• Difficulty breathing or shortness of breath 
• Discomfort when breathing while laying down 
• Chest fullness 
• Fever and/or chills 
• Fatigue 
• Painful joints 
• Changes in heart rhythm 
• Enlarged heart size on chest X-ray 
• Abnormal pericardial appearance on echocardiogram

An initial set of tests performed on a sample of pericardial fluid helps determine whether the fluid is a transudate or exudate.

Transudate:

• Physical characteristics—fluid appears clear
• Protein or albumin level—decreased
• Cell count—few cells are counted

Transudates usually require no further testing. They are most often caused by either cirrhosis or congestive heart failure.

Exudate:

• Physical characteristics—fluid may appear cloudy
• Protein or albumin level—higher than normal
• Cell count—increased

Exudates can be caused by a variety of conditions and diseases and usually require further testing to aid diagnosis. Exudates may be caused by, for example, infections, trauma, various cancers, or pancreatitis. The following is a list of additional tests that the doctor may order depending on the suspected cause:

Physical characteristics – the normal appearance of a sample of pericardial fluid is straw coloured and clear. Abnormal results may give clues to the conditions or diseases present:

• Milky appearance—may point to lymphatic system involvement
• Reddish pericardial fluid may indicate the presence of blood
• Cloudy thick pericardial fluid may indicate the presence of microorganisms and/or white blood cells

Chemical tests –in addition to protein or albumin, a glucose test may be performed. Glucose in pericardial fluid samples is typically about the same as blood glucose levels. It may be lower with infection.

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 may be performed to look 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 - used 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. 
• Under certain situations, such as prior antimicrobial treatment or if viral infection suspected, the synovial fluid may be tested using molecular techniques to detect micro-organism DNA/RNA. This can help detect dead organisms or low numbers of organisms. This test may need to be sent to a reference laboratory to be performed.  
• Adenosine Deaminase - rarely, this test may be used to help detect tuberculosis. If the level is markedly elevated in pericardial fluid in a person with symptoms suggesting tuberculosis, makes it likely that the person has Mycobacterium tuberculosis infection in the pericardiam. 

Other tests for infectious diseases that are less commonly ordered may include tests formycobacteria (AFB smear and culture), and parasites. 

Increased amounts of pericardial fluid also can restrict the movement of the heart. Cardiac tamponade is when pericardial fluid builds up 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. 
 
A blood glucose, protein, or albumin  may be requested to compare concentrations with those in the pericardial fluid. 

Blood serology tests may also be sent to look for changes in antibody levels to certain viruses, indicating current or recent infection that may have caused the pericarditis.  

Pericardiocentesis is the removal of pericardial fluid from the pericardial sac with a needle and syringe. An intravenous (IV) line may be inserted 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.