Joint fluid culture is a laboratory test to detect infection-causing germs in a sample of fluid surrounding a joint.
A sample of joint fluid is needed. This may be done in a doctor's office using a needle, or during an operating room procedure. Removing the sample is called joint fluid aspiration.
The fluid sample is sent to a laboratory. There, it is placed in a special dish and watched to see if bacteria, fungi, or viruses grow. This is called a culture.
If these germs are detected, other tests may be done to further identify the infection-causing substance and determine the best treatment.
Your health care provider will tell you how to prepare for the procedure. No special preparation is needed. But, tell your provider if you're 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.
Sometimes, the 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 discomfort if the tip of the needle touches bone. The procedure usually lasts less than 1 to 2 minutes.
Your provider may order this test if you have unexplained pain and inflammation of a joint or a suspected joint infection.
The test result is considered normal if no organisms (bacteria, fungi, or viruses) grow in the laboratory dish.
Abnormal results are a sign of infection in the joint. Infections may include:
Risks of this test include:
Reviewed By: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.