How the Test is Performed

A sample of synovial fluid is needed for this test. Synovial fluid is normally a thick, straw-colored liquid found in small amounts in joints, bursae (fluid-filled sacs in the joints), and tendon sheaths.

After the area is cleaned, the health care provider will insert a sterile needle through the skin and into the joint space. Once the needle is in the joint, fluid is drawn through it into a sterile syringe.

The fluid sample is sent to the laboratory. The laboratory technician will:

• Check the sample's color and clarity
• Place it under a microscope, count the number of red and white blood cells, and then look for crystals (in the case of gout) or bacteria
• Measure glucose, proteins, uric acid, and lactic dehydrogenase (LDH)
• Culture the fluid to see if any bacteria grow

How to Prepare for the Test

Normally, no special preparation is needed. Tell your health care provider if you are taking blood thinners, because they can affect test results or your ability to take the test.

How the Test Will Feel

Sometimes, the health care provider will first inject numbing medicine into the skin with a small needle, which will sting. A larger needle will be used to draw out the joint fluid or synovial fluid.

This test may also cause some pain if the tip of the needle touches bone. The procedure usually lasts less than 1 to 2 minutes.

Why the Test is Performed

The test can help diagnose the cause of pain, redness, or swelling in joints.

Sometimes, removing the fluid can also help relieve joint pain.

This test may be used when your doctor suspects:

• Bleeding in the joint after a joint injury
• Gout and other types of arthritis
• Infection in a joint

What Abnormal Results Mean

Abnormal joint fluid may look cloudy or abnormally thick.

Blood in the joint fluid may be a sign of injury inside the joint or a body-wide bleeding problem. An excess amount of normal synovial fluid can also be a sign of osteoarthritis.

Risks

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

Considerations

Ice or cold packs may be applied to the joint for 24 to 36 hours after the test to reduce the swelling and joint pain. Depending on the exact problem, you can probably resume your normal activities after the procedure. Talk to your health care provider to determine what activity is most appropriate for you.

Alternative Names

Joint fluid analysis; Joint fluid aspiration

References

El-Gabalawy HS. Synovial fluid analysis, synovial biopsy, and synovial pathology. In: Firestein GS, Budd RC, Harris ED Jr, et al, eds. Kelley's Textbook of Rheumatology. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 48.

Parrillo SJ, Marrison DS, Panacek EA. Arthrocentesis. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 5th ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 53.

Update Date: 4/4/2012

Reviewed by: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Dept of Orthopaedic Surgery. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.