Synovial fluid analysis

Definition

Synovial fluid analysis is a group of tests that examine joint (synovial) fluid. The tests help diagnose and treat joint-related problems.

Alternative Names

Joint fluid analysis; Joint fluid aspiration

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, 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 in the joint, fluid is drawn through the needle into a sterile syringe.

The fluid sample is sent to the laboratory. The laboratory technician will check the sample's color and clarity, and then place it under a microscope to check it for red and white blood 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.

How to prepare for the test

Normally, no special preparation is necessary, but contact your health care provider before the test to make sure. Tell your doctor if you are taking blood thinners, as they can affect test results.

How the test will feel

Occasionally, the health care provider will first inject local anesthesia with a small needle, which will sting. The aspiration is done with a larger needle and may also cause some pain. The procedure usually lasts less than one minute.

Why the test is performed

The test can help diagnose the cause of pain or swelling in joints. Removing the fluid can also help relieve joint pain.

This test may be used to diagnose:

• Gout
• Infection
• Other inflammatory joint conditions
• Joint injury
• Osteoarthritis

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.

What the risks are

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

Special 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.

References

Knight JA, Kjeldsberg CR. Cerebrospinal, synovial, and serous body fluids. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 28.