The Test Sample
What is being tested?
Synovial fluid is a thick (viscous) liquid that acts as a lubricant for the major joints of the body. It is found in small quantities in the spaces between the joints, where the fluid is produced and contained by synovial membranes. Synovial fluid cushions the bone ends and reduces friction during joint movement in the knees, shoulders, hips, hands, and feet.
Synovial fluid analysis consists of a group of tests that detect changes in synovial fluid that may indicate the presence of diseases that affect joint structure and function. It usually involves an initial basic set of tests, followed by additional tests that are selected based upon the results of the first set of tests, the person's symptoms, and the disease that the doctor suspects is the cause of the symptoms. Tests can be grouped according to the type of exam that is performed into:
- Physical characteristics—an evaluation of the appearance of the fluid
- Chemical tests—detect changes in the chemical constituents of the fluid
- Microscopic examination— cells and crystals that may be present are counted and identified by type under a microscope
- Infectious disease tests—detect and identify microorganisms, if present
How is the sample collected for testing?
A sample of synovial fluid is collected by a doctor from the affected joint with a syringe and needle using a procedure called an arthrocentesis.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Consult with the doctor about test preparation. Synovial fluid collection and analysis may be performed after fasting or at random.