Synovial fluid analysis
Synovial fluid analysis is a group of tests that examine joint (synovial) fluid. The tests help diagnose and treat joint-related problems.
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 (fluid-filled sacs in the joints), and tendon sheaths.
After the joint area is cleaned, the health care provider inserts a sterile needle through the skin and into the joint space. Fluid is then drawn through the needle into a sterile syringe.
The fluid sample is sent to the laboratory. The laboratory technician:
- Checks the sample's color and clarity
- Places the sample under a microscope, counts the number of red and white blood cells, and looks for crystals (in the case of gout) or bacteria
- Measures glucose, proteins, uric acid, and lactic dehydrogenase (LDH)
- Cultures 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 a blood thinner, such as aspirin, warfarin (Coumadin) or clopidogrel (Plavix). These medicines 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 is then used to draw out the 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 or cartilage injury.
- Infection of the joint -- unusual but more common with repeated aspirations
- Bleeding into the joint space
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.
El-Gabalawy HS. Synovial fluid analysis, synovial biopsy, and synovial pathology. In: Firestein GS, Budd RC, Gabriel SE, et al., eds. Kelly’s Textbook of Rheumotology. 9th ed. Philadelphia, Pa.: Elsevier Saunders; 2012:chap 53.
Parrillo SJ, Marrison DS, Panacek EA. Arthrocentesis. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 5th ed. Philadelphia, Pa.: Elsevier Saunders; 2009:chap 53.