Pericardial Fluid Analysis
A variety of conditions and diseases can cause inflammation of the pericardium (pericarditis) and/or excessive accumulation of pericardial fluid (pericardial effusion). Pericardial fluid analysis comprises a group of tests used to determine the cause. There are two main reasons fluid may collect in the pericardial space:
- Fluid may accumulate because of an imbalance between the pressure within blood vessels—which drives fluid out of blood vessels—and the amount of protein in blood—which keeps fluid in blood vessels. The fluid that accumulates in this case is called a transudate. Transudates are most often caused by cirrhosis or congestive heart failure.
- Fluid accumulation may be caused by injury or inflammation of the peritoneum, in which case the fluid is called an exudate. This type of fluid may be the result of conditions such as infection, malignancies (metastatic cancer, lymphoma, mesothelioma), rheumatioid disease, or systemic lupus erythematosus.
Differentiation between the types of fluid is important because it helps diagnose the specific disease or condition. Doctors and laboratorians use an initial set of tests (cell count, protein or albumin and appearance of the fluid) to distinguish between transudates and exudates. Once the fluid is determined to be one or the other, additional tests may be performed to further pinpoint the disease or condition causing pericarditis and/or pericardial effusion.
How is the sample collected for testing?A sample of fluid is collected from the pericardial sac by a doctor with a syringe and needle using a procedure called a pericardiocentesis.
Is any test preparation needed to ensure the quality of the sample?No special preparation is usually needed.
How is it used?Pericardial fluid analysis is used to help diagnose the cause of inflammation of the pericardium called pericarditis and/or fluid accumulation around the heart (pericardial effusion). There are two main reasons for fluid accumulation and 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:
- An imbalance between the pressure within blood vessels (which drives fluid out of the blood vessel) and the amount of protein in blood (which keeps fluid in the blood vessel) can result in accumulation of fluid (called a transudate). Transudates are most often caused by cirrhosis or congestive heart failure. If the fluid is determined to be a transudate, then usually no more tests on the fluid are necessary.
- Injury or inflammation of the pericardium may cause abnormal collection of fluid (called an exudate). Exudates are associated with a variety of conditions and diseases and several tests, in addition to the initial ones performed, may be used to help diagnose the specific condition including:
- 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.
- 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.
- Cancer – such as mesothelioma that has arisen in the pericardium or metastatic cancer that has spread to it.
When is it ordered?Pericardial fluid analysis may be ordered when a doctor suspects that a patient has a condition or disease that is causing pericarditis and/or pericardial effusion. It may be ordered 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
- Difficulty breathing
- Changes in heart rhythm
- Enlarged heart size on chest X-ray
- Abnormal pericardial appearance on echocardiogram
What does the test result mean?An initial set of tests performed on a sample of peritoneal fluid helps determine whether the fluid is a transudate or exudate.
- Physical characteristics—fluid appears clear
- Protein or albumin level—decreased
- Cell count—few cells are counted
- 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 in the 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 colored and clear. Abnormal results may give clues to the conditions or diseases present and may include:
- 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 tumor 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—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.
Is there anything else I should know?Increased amounts of pericardial fluid also 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 buildup can be a medical emergency, causing heart failure and death. When fluid accumulates slowly, the pericardial sac stretches and symptoms gradually worsen.
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 anesthetic 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 may be used to help guide the needle.
Are there other reasons to do a pericardiocentesis?Yes. Sometimes it will be performed to drain excess pericardial fluid – to relieve pressure on the heart and/or to aid in the treatment of an infection. Sometimes a catheter drain is left in place for a period of time to remove larger amounts of fluid and to drain recurrent fluid accumulations. Sometimes medications will be introduced into the space during the pericardiocentesis.