A culture of joint fluid, or aspirate, can identify bacteria or organisms in joint fluid that may be causing an infection in a particular joint. The test is normally done when a joint is swollen, painful, or appears to be infected.
This test is normally performed to help diagnose arthritis, or an infection in a joint.
First, a sample of fluid is taken from the swollen joint. The skin overlying the joint will be anesthetized with a local anesthetic, such as lidocaine, and then be carefully cleansed before the procedure is performed.
Then, a sterile needle is inserted through the skin into the joint. A small amount of fluid is withdrawn from the joint.
This sample is sent to a laboratory for testing. Usually, the fluid is then placed on special culture media to see if bacteria or other microorganisms will grow.
There is no specific preparation required for this test. A person should request specific instructions from his or her health care provider.
Fluid in a joint is usually sterile. This means that no microorganisms are present. If the joint fluid contains microorganisms, such as bacteria or fungi, they will grow in culture in the laboratory. This allows a microbiologist to identify the microorganisms and design a course of therapy to treat the infection. For example, a bacterial infection would be treated with antibiotics.