Joint fluid culture is a test performed on a specimen of the fluid surrounding a joint. It is used to identify organisms that cause infection. See also synovial fluid analysis.

A sample of joint aspirate or fluid is removed from the joint with a needle or in the operating room, then is placed on culture media in containers for the purpose of growing microorganisms (bacteria, fungus, or viruses) in the laboratory.

The microbiologist in the laboratory inspects the cultures daily for growth. If microorganisms are detected, other tests may be initiated to identify the infectious agent and determine the sensitivity of the organisms to medications. Antibiotic therapy can then be determined based on these results.

There is no special preparation necessary.

The sample may be obtained in the health care provider's office or in the hospital. The skin over the joint is cleansed with antibacterial soap. A local anesthetic may be injected into the skin over the joint. The injection may burn or sting.

After the area has become numb, a larger needle is inserted into the joint, and fluid is withdrawn. There may be pressure in the joint. Some minor soreness may be present for several days.

The test may be performed when there is unexplained pain and inflammation of a joint, or suspected infection in a joint.

The presence of no organisms in the culture (a sterile culture) is normal.

Abnormal results indicate an infection in the joint. The infection may be bacterial, mycobacterial, or fungal. The results tell the doctor which organism is causing the infection. This helps determine the most effective medication.

Other associated conditions:

• Fungal arthritis
• Non-gonococcal (septic) bacterial arthritis
• Gonococcal arthritis

The risks are introducing an infection or bleeding in the joint.

Not applicable.