To obtain the fluid for analysis, a sterile needle is inserted into the joint space through skin that has been specially cleaned. Once in the joint, fluid is aspirated through the needle into a sterile syringe.

Synovial fluid is normally a viscous (thick), straw colored substance found in small amounts in joints, bursae, and tendon sheaths. In the laboratory, the fluid is initially analyzed for color and clarity. It is then examined microscopically for cells (red and white cells), crystals (in the case of gout), and bacteria. In addition, there may be a chemical analysis, and if infection is a concern, a sample will be cultured to see if any bacteria grow.

Abnormal joint fluid may look cloudy or abnormally thick.

Normally, no special preparation is necessary, but contact your health care provider before the test to make sure.

Infants and children:
The preparation you can provide for this procedure depends on your child's age, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following:

• Infant test or procedure preparation (birth to 1 year)
• Toddler test or procedure preparation (1 to 3 years)
• Preschooler test or procedure preparation (3 to 6 years)
• Schoolage test or procedure preparation (6 to 12 years)
• Adolescent test or procedure preparation (12 to 18 years)

The test is performed to diagnose the cause of pain or swelling in joints, and to relieve pain from fluid accumulation (usually blood or pus) in the joint.

Common diseases diagnosed with fluid aspiration include infection, gout, and other inflammatory joint conditions. Blood in the joint may be an indication of trauma inside the joint or a systemic bleeding problem. An excess amount of normal synovial fluid can also be a sign of osteoarthritis.

• Infection of the joint -- unusual but more common with repeated aspirations
• Bleeding into the joint space